About a year and a half (maybe two?) ago we purchased a dual socket opteron 4386 for use as a build machine. A lot of this was based on the fact that we only had like $1500 to spend and we wanted the most bang for the buck. The spec gcc benchmarks showed the CPU doing quite well against significantly more expensive intel machines. So, we jumped on it, and haven't regretted it for a minute. Its a good combination of lots of cores and fast single threaded performance (for the linking and packaging). Combined with the SSDs and ECC RAM, its quite a screamer.

We have a number of intel machines for other purposes, and it still costs probably about 2x in intel land to get a machine to beat it. Maybe closer to 3x if you buy the machine from HP/IBM.