Well deicated multiprocessors are always better than SMT, or simultaneous multithreading AKA Hyperthreading, though your wallet will pay for it. As far as improving performance, it would only improve performance on applications that are dual processor aware, such as Photoshop and Windows. Im not sure of any games specifically that are dual processor aware, though Im sure someone can enlighten you on this subject. So as far as overall system performance is concerned, dual processing is great. It wont do the fabled "combined clock speed" performance leap but youll see a definite performance enhancement, especially if you use very new dual processor capable chips like the Opteron. Of course, as a rule of thumb, dont buy two dual processor chips whose combined clockspeed can be matched or exceeded by a single processor, especially one from Intel with SMT. So you shouldnt buy two Athlon MP 2000+ chips in lieu of a 3.0GHz P4 w/ HT because the performance wouldnt be much greater compared with the price difference.