In my post Cutting off the Rhubarb's Flower Bud: what are we missing? I included a picture of said flower and pointed out that it wasn't really worth the wait. The other reason you shouldn't let your rhubarb flower is that it could well be the end of the plant.
Which is what happened to mine. The plant pictured died down for winter, never to be seen again. It had always been a weakling anyway, being Glaskins Perpetual grown from seed.
It takes some time for seed-grown rhubarb to bulk up enough to produce a good number of sticks (I'd personally say longer than the two years suggested on The Rhubarb Compendium, a comprehensive and excellently referenced site, but I didn't exactly cosset my plant).
We still have a plant of Glaskins Perpetual, around eight years on, and although it does now produce numerous sticks, they are spindly affairs that mean you need twice as many as you might pick from, say, a Victoria. On the whole, I'd go for planting crowns of rhubarb (that's the root part, if you're not sure), widely available in seed catalogues. Altogether more robust, producing thicker stalks.
Meanwhile, rhubarb is one of those crops that engenders particular enthusiasm in some quarters and has several websites dedicated to it. One of the most fun is Savor the Rhubarb, run by Elizabeth, who lives in Georgian Bay, near Toronto, Canada. You never quite know what you'll turn up on her site. Apart from a wide variety of lovely sounding recipes and useful information on growing and picking, she includes rhubarb craft, links to artwork and gems such as the desert-dwelling Self-Watering Rhubarb and The Rhubarb Tart song performed by John Cleese. (And for the lyrics to that, see Humor Links.)
And if you think John Cleese should have kept his mouth shut (singing - not his strong point), you'll find Bill Oddie, from the 1960s radio show I'm Sorry I'll Read That Again (still playing on Radio 4 Extra) far more melodious in his own song about Rhubarb Tart: