Tonight I installed Fedora 15 onto a system that is SSE3 capable and ran Left 4 Dead 2. The server install is identical to the one on the server that broke as is the distro itself. The server started perfectly. Valve is requiring SSE3 now leaving those of us running older systems in the dust.
Thank you Valve for being so caring about the people who take the time out of their lives to run the stuff you put out. /endsarcasm
Update
The problem has been fixed for awhile now. I thought I should update.