In reply to:
I do find it useful to have multiple cpu cores for when one of my processes goes runaway! 
That is one of the first things I noticed when I upgraded to a Core 2 Duo. The software that came with my HD-TV tuner occasionally decides to get itself into some sort of loop and locks the CPU at 100% usage. On my previous P4, the system would become totally unresponsive when this happened, making the task of shutting down the process frustrating. However, on the C2D only one core goes to full usage and the system stays responsive, making it easy to shutdown the errant process.
As for browser speed; I think it is a case of 'perceived speed'. When I moved from IE6 to Firefox, the first thing I noticed was that IE6 'felt' faster at rendering pages than Firefox. After a little experimentation, I discovered that both browsers were basically taking the same amount of time to render a given page, but IE6 was buffering the page contents and rendering the whole thing at once, while Firefox was rendering each page element as it was pulled down. This created the perception that IE6 was faster (well at least to me
). A little tweaking of the 'nglayout.initialpaint.delay' setting in Firefox fixed the issue and now both browsers appear to render at the same speed to me.
Mark