I've been wearing VFFs almost exclusively* for the last year. I started by just wearing them to walk around in, wearing them to work and so on, then started running in them for short distances, gradually building up to being able to do 10K races in them about 9 months later. Whether they've really changed my form or not, I don't know — I think I've always been a mid-foot striker, but I do know that my recurring ITB injury doesn't flare up when I'm wearing them.
Incidentally, if you're going to the US any time soon, buy them there — they're way cheaper and more readily available to try on! Also bear in mind that sizing can vary between different styles.
As for the comments about "you weren't designed to run on concrete" - as someone else mentioned earlier, sun-baked dry, compacted earth is pretty damn hard and there is no reason why, with optimal running form, your body can't absorb the impact.
For what it's worth, I think there are a few reasons why VFFs might not be worn (at least publicly) by professional athletes. First, I doubt Vibram can offer as much sponsorship money as Nike and Adidas and second, switching to minimal shoes requires a long transition period if you're going to do it without injury and I don't think they'd want to risk that in their training schedule.
* I switched back to my 'normal' running shoes for longer distance training/racing while I was building up the mileage in VFFs.