What's the date today? Are you sure? A cursory glance at this pic of Sienna Miller on the right, and you'd be forgiven for thinking we'd travelled back to 2004.

For while the spring/summer 09 collections have thrown up myriad trends for summer — printed leggings, studded gladiators, leather biker jackets, to name but three — boho isn't one of them.

Yet, spotted walking along the King's Road the other day, Sienna Miller looked the quintessence of boho chic, as though the past five years had never happened. Which, if you consider this picture in the centre — taken in May 2004 — they may as well not have.

Back then, Miller didn't just wear the boho look: she was the boho look. Every trend has its poster girl, and if Kate Moss was the figurehead for skinny-jeaned rock chic, Sienna Miller was the wafty skirted equivalent.

As anyone tall, pale or ungainly who has ever tried to wear a ra-ra skirt will attest, boho works best on life's petite, sun-kissed blondes, the sort of girls for whom fake tan streaks are an anathema and life is one long, hot August bank holiday.

So compelling was Sienna in her role of cowboy boot-wearing boho princess that thousands of us felt the urge to try it, festooning ourselves in tiered skirts, studded belts, ethnic bangles and pendants picked up on a flea market in Ibiza Town.

Some might say that Sienna's ditsy floral dress, smoky shades and shaggy hair speak of nothing more than that she is stuck in an almighty style rut. But it is significant that Sienna has returned to the look that first defined her. Her messy private life seemed to result in a sort of style schizophrenia: in recent months, we have had Scruffy Sienna, Sloaney Sienna and Sluttyenna, as the travails of her love life were mirrored by her wardrobe.

By going back to boho, perhaps Sienna is finally at peace, both with herself and with the fact that she looked rubbish as a corporate Hollywood blonde. Let's just hope the rest of us don't feel compelled to follow suit.