well for those who are planning to buy new desktop computer here are some cpu  on what to avoid 

Pentium 4 
Extremely power hungry, nothing special in terms of performance. 

Pentium D 
(except the 805 model) 
Extremely power hungry (especially the 8xx series), poor performance compared to Athlon 64 X2 and Core 2 Duo 

Athlon 64 FX 
Solid performers, but poor price/performance ratio. 

Phenom Quad Core: Two Steppings B2 & B3 
General: Attractive price, especially for a quad core, but has/had know problems and inconsistant performance.’Unverified’…purchase at your own risk 

B2 Stepping: Known to be subject to the TLB “bug”-Translation Lookaside Buffer. This problem MAY occur during maximum loading of all cores under virtualization 
AMD offers a fix, or workaround, which inccurs a 10~20% decrease in perfromance 

B3 Stepping: Second retail production stepping of the ‘Phenom’ series of AMDs. This stepping was created/released to addresss the TLB Bug and correct it. Currently, inconsistant reports regarding the success of B3 in correcting the TLB bug, along with reported problems of ‘core 2′ place this processors in the “Buy at your own risk” catagory. 
As these chips filter into the market, and more unbiased user reports appear, this chip may very well find its way to the ‘highly recommended’ catagory, but for now, it is too new for its reliability to be proven. 

source: tomshardware