It looks good to me, although there is some noise in various enthusiast forums about how the new (and quickly discontinued) socket 939 opteron processors have a price/performance overlap at the 3700 San Diego point. Basically you can get a socket 939 opteron cpu that runs the same speed as the 3700 San Diego, for less money. One benefit appears to be that while the socket 939 opterons are nearly identical to the San Diego processors, they are considered "cherry" cpus due to more rigorous testing standards used for the server cpus. There are rumors about a better memory controller in the opterons as well, but I haven't seen any specifics about that.
But basically before you buy a socket 939 A64 3700 San Diego, take a look at the socket 939 opteron running at the same clock speed. If it's cheaper, get the opteron.
Right now on newegg, the opteron 148 and A64 3700 San Diego processors are the same price ($235), but you can get an OEM Opteron 148 for $229 if you already have a good A64 HSF. Or take a look at the Opteron 150s for just a bit over $300. Newegg doesn't have the best prices so you might find an opteron 148 somewhere else at a cheaper price.