Wow, I'm so surprised that this is still on the front page AND has over a thousand views...
I suppose I'll give an update, considering I'm here..
I got the cheaper model, and it ran WoW well enough, 60 FPS in dead areas, 20 in Dalaran, unfortunately after a few addons/if I had ANYTHING running in the background, stuttering was very bad
As for L4D, there are times when I can tell it's having issues, but I was honestly having more problems with my internet connection not being up to snuff than the machine.
Last week I bought 4 gigs of ram, and upgraded it, I can now say that my mac mini is probably the ugliest Mac product ever, the bottom side of it has over a hundred scratches, leftover putty, and I'm pretty sure I messed up some of the pins (though, that could just be my imagination), if you can't handle a single scratch on your mini, I'd def get the pros to upgrade your ram
On the inside, the mini is really fantastic, the way they put all that in there, just amazing, pictures really don't do it justice, will say though, foam is magic for the small formfactor machines apparently, there was quite a bit of foam doing things such as reducing noise, vibration, and directing air flow. And those snap off connectors were awesome, I accidentally got the Airport's wire wrapped around something, and when I pulled the top part off, it actually pulled out, which led to several seconds of "omigawd what did I just do?!" then realizing it just pops back
I'm sorry, I just.... went off on a tangent there, but, haven't gotten a chance to try L4D yet, but now I get 60 FPS in Dalaran full of people, 30 FPS recording, but I that's what I capped it at, and this was in/around Dalaran as well, view distance 50%, Environment detail 100%, and I can listen to iTunes on the Mac Mini's speakers now, working slowly on upgrades for it, unfortunately due to various tech things dying on me it's slow going