In reply to ed34:
I love my gri-gri, but IMHO it's a pretty specific tool.
Great when you expect your climbing partner to be working a route, dogging it, resting it, falling off and wanting to be hauled back up, etc. plus a couple of other specific circumstances. Generally I'll still use my ATC for about 90% of my climbing, but the labour savings it makes on the other 10% is totally worth it.
The main drawback is paying out slack quickly without letting go of the dead rope, which is initially tricky to get the hang of. (The Petzl 'new technique' works well) You do just need to pick up the knack with it, though, and it's fine.
If you belay with it properly (ie. not hanging on to the lever) then I can't see that 'panic grabbing' is an issue.
Even so, I still use my ATC to belay partners on redpoint attempts as it's always going to be marginally quicker to pay slack rope out.
Think of it as a mechanically-assisted belay device, not an automatic device, and you'll be reet.
Officially you're not meant to use it with skinny ropes, but in practice it works on my 9.5mm rope fine. I know people who use it on ropes down to 9.2mm - but you pays your money you takes your chances.