Stealth and a couple others have reported some laggyness in a few maps, when >2 players on the server or something like that. In xt4zy-med01 the problem was a lot more widespread. Playing it locally I get 300+ fps, but on a server with a few people I also get drops to like 30fps and such. I'm somewhat sure it has to do with collision detection and brush counts. I'll come up with a fix in a few days. I'm prioritizing the "Development" system (bug/idea tracker) now.
You better! *Shakes fist*
Actually, I ended up doing a temp/quick fix for it tonight, at least it fixes the problem I was able to reproduce.. So yeah, will push that out and get feedback on it, pending a permanent fix :)