I would be very happy if 15% was true. But I think it's around 5% max. There are customers who look for AMD specifically but they are very rare. I see one ( if lucky) AMD server out of 1000.
for my company it comes down to heat and power consumption. In many things the opterons do just as well, after all in visualization, sql, etc more cores = mo better. But when you can get a 65w or less xeon to do the same job as a 125w opteron you're going go with the lower power consumption and less heat model. When you're running your own rig you may not notice too much. But at a co-location with thousands of servers, you're going to friggin notice, and so is your power bill.
