They do run hot. If you are smart, you will design your system with an exceptional cooling capacity, such as I have done with my main box.
Thermalright SK6's are great heatsinks - 70 fins, all copper. My temperature doesn't rise above 38ºC. However, the fans are also important. Black label Delta's - 38CFM from a 6CM fan.
They are <b>loud</b>. But the system is <b>fast</b> and <b>cool</b>. It is worth it.
Just some things to keep in mind when building an Athlon.