I've been playing with Untangle for a few weeks now and finally put a box in front of my entire network earlier today (if only for a short time).

I'm running UT on a Dell Optiplex GX270, P4 2.8 with 1GB RAM, I was running the content filter, attack blocker, router, protocol blocker, and spyware blocker on a network with approx. 1000 computers, and it handled the load every bit as well as our sonicwall. If it wasn't for one problem that we're having (see my post about weird wan problems in the general forum), the sonicwall would still be off the network and we'd probably have a permanant place there for an untangle box. We'll see how it goes trying to resolve the issue, I'm sure it's probably something simple.