Books: who needs them? When you've got the internet, dvds and CD-Roms, as well as those older foes of reading, TV and film, why bother with these clumsy, laborious artefacts of wood pulp and printer's ink? It follows that if we don't need books, who needs libraries?

The library of Alexandria, one of the seven wonders of the ancient world, contained in its mighty structure an infinitesimal fraction of the data you can reach in seconds via Google.

As for the puny library in your high street, with its amiable Victorian architecture, shabby décor and coughing derelicts, its information storage capacity was left behind by personal computers some time in the Eighties.

A recent report by the former Waterstone's director Tim Coates entitled Who's in Charge? claims that "there may be no libraries in 10 to 15 years' time"; he supports his argument with graphs showing a steady decline in use. Government has also decided that libraries are in trouble.

Last month, Culture Secretary Tessa Jowell declared that they must "involve, engage and inspire their customers", she also announced that the less-thaninspiring sum of £2 million would be made available to help Britain's 2,500 libraries.

I visited two new, architect-designed libraries last week. One of them, 17 storeys high and magnificent, was designed by the Dutch architect Rem Koolhaas for the centre of Seattle, the city of Microsoft. The other, more modestly-scaled, is in Chrisp Street Market, east London, and is designed by the British architect David Adjaye.

Koolhaas, 59, has now entered a stratosphere of fame and glamour, with a string of celebrities - Brad Pitt, Jennifer Aniston, Robert De Niro, Leonardo DiCaprio - turning up to last week's opening dinner for his LA Prada store. Adjaye, 37, architect to Chris Ofili and other stars of Britart and fashion, is rapidly heading in the same direction.

Neither of these architects was likely to confirm the conventional image of libraries as fusty places, and both were briefed to design the modern kind of library that gives access to computer terminals, as well as books.

Adjaye's library is one of seven "Idea Stores" that the London Borough of Tower Hamlets has commissioned to be "bright new buildings", offering "comfortable friendly surroundings" and "quality, good service and fun". The first Idea Store was the refurbishment of an existing building in Bow; Chrisp Street, the second, has been designed from scratch.

They are called Idea Stores for fear that the word "library" is too offputting, and also to reflect the intention that libraries should, when it comes to attracting the public, learn a thing or two from shops.

All the Idea Stores are to be placed in shopping areas, as local residents were put off by libraries' inaccessible locations: Chrisp Street Market will be followed by a larger Idea Store next to Sainbury's in Whitechapel.

These "stores" aim to shift their goods - enlightenment, nourishment for the soul, whatever - in the same way that Tesco shifts Kenyan runner beans and multipacks of Fanta.

The concept teeters on the brink of crassness, and I say this as one who abetted the process by sitting on the competition jury that chose Adjaye. There is the whiff of the trendy vicar to it, as he desperately tries to make religion "relevant".

Worse, it threatens to betray the beauty of libraries as one of the last places of peace and reflection that have not been consumed by the voracious god, Retail.

It is also an assault on Koolhaas's belief that "the library represents, maybe with the prison, the last of the uncontested moral universes". As museums, he implies, have become ever more mall-like and infested with shops, libraries retain the ability to set out some high-minded values.

But the unashamed retail ideology behind the Idea Stores leaves only the likes of Wormwood Scrubs and Pentonville as his "moral universes".

It is a relief to report that there is nothing mall-like about the Chrisp Street Market Idea Store, which opened to the public yesterday. The £3 million building seeks to charm but not ingratiate, to attract but not compel.

The exterior is mostly glass, with panels in five shades of green and five of blue, like sophisticated boiled sweets. Adjaye aimed for "a certain kind of beauty that communicates". It is shop-like because "good shops give you the desire to be in them"; the Idea Store is trying to do the same, but it does not drive you to focus solely on the product, as a shop would.

Set in a heavy concrete shopping centre and housing estate, the glassy building is light and translucent where the surroundings are opaque and matt. As something shiny, it has more in common with the towers of Canary Wharf that loom to the south, and it seems to conform to the modern convention that regeneration is best symbolised by wipe-clean surfaces.

But there is subtlety here, as Adjaye sets the classy glass of the outside against rougher and plainer materials (recycled plywood and concrete) within the building.

Inside, stairs and escalators lead up to a long oblong hall where, apart from a rubber floor, timber is the dominant material. The recycled plywood has a workmanlike roughness to it.

It forms the exposed beams of the ceiling - like a modern take on the Tudor house - and the shelves which curve into S-shapes and break up the space. Adjaye says he wanted to create "a grand civic space" that would also be a place "to meander". This freedom to find your own way is exactly what reading, and libraries, should offer.

Meanwhile, in Seattle, Koolhaas has produced the building of his career, described by the architecture critic of the New York Times as the best he had ever seen.

Eight times as tall as Adjaye's library and, at $167 million, costing many times as much, it has instantly become Seattle's most significant public building. Amid the mute, closed office towers of the city's business district, it is an irregular crystal that activates its surroundings with unexpected reflections and projections, and views into its generous interior.

The building encloses an internal landscape of decks and terraces and, with sunlight falling through a latticed steel-and-glass skin, it provides an artificial equivalent of the mountain ranges that ring Seattle.

At moments, the library leans forward to catch a view of water or the snow-capped Mount Rainier; at others, it creates cavelike rooms buried deep inside.

Here, what Adjaye calls " meandering" becomes an almost infinite journey of discovery, a hike through ever-changing spaces. Like the Idea Store, it also plays rough against smooth - from its shiny glass to the bubbled, black fireproof paint on its internal steel columns.

Of course, architecture in itself is not enough: libraries need books more than they need design and Seattle and Tower Hamlets must match their architectural ambitions with expanding their stock.

But these two buildings, so far apart in place and scale, both restore faith in the library. They are truly public places that allow people to think and do as they please and which also have the sheer sex appeal to attract new users.

The only fly in the ointment is the crude, large-type announcement on the façade of the Idea Store pronouncing that it is "sponsored by Lloyds", which almost makes the whole thing look like a bank. More munificent donors to the Seattle library are far more discreet, so why does Lloyds have to shout so loud?