I love my Vibrams. Been running for five or six years now, distances from 10k to a 52km ultra marathon in South Africa - so I like to think I at least know a little of what I'm talking about.
My Vibrams were a little tight to begin with, but over time they've loosened up a bit and now they're just a perfect fit. They're a nightmare to put on and take off the first few times, but persevere - you'll get used to it. And the first run you have with them - wow. Seriously, they're awesome. You can feel the texture of whatever's underneath you, and also the cold or warmth transferring to your foot. As they're ridiculously light, you'll notice within just a few runs the difference in weight as soon as you put your old trainers back on.
A couple of warning:
1. It's easy to stub your toe on the ground if you're not careful, I've done it twice now. Nothing broken, just painful for a few minutes, though fortunately I could run through mine.
2. Heel strike. If you heel strike then you'll struggle initially in these. I tend to mid-foot strike so I've been lucky, but if you heel strike you'll have to adapt your running style, although this should happen naturally. But if that's the case, don't go out for long runs straight away in them, let your feet adapt. There are lots of other articles on this issue that explain it better than I can, so just google Vibrams and heel strike.
3. The cloth material at the top. Mine is looking a little tatty now. Not hugely, but there are a couple of tiny rips from where I've been running cross country and my foot has brushed against something on an overgrown trail. Not a big issue, but it's a bit of a shame. When I say a little tatty, though, I mean just that - don't get all paranoid they won't last, they most definitely will.
4. Social. Be prepared for lots of stares and questions!