So far I have it running on a P3-450 w/ 512MB ram, no users yet but I'm considering seeing about putting a few users in to see how it does. The only problem with install I had was with fedora core 5 naming libssl.so.5 and libcrypt.so.5 /lib/libssl.so.0.9.8a and /lib/libcrypt.so.0.9.8a symbolicly linking libssl.so.5 and libcrypt.so.5 to these and running ldconfig resolved these issues. This will also be a good test to see how well my home server (k6-2 450) will handle the very few users i host. My production server is a dual opteron box with 4gig of ram on Suse EL 9. I like what I've seen so far with 4.01. The problem with upgrading, is we have about 1700 - 1800 users on it and have had some problems with pop3 dieing intermittently, i've upped it to 40 pop3 connections and it seems to be helping as today was the first time it's crashed since I made the change, and at this point I can't say it's not due to me installing a commercial ssl certificate (that I think I generated wrong but that's a different thread).