The biggest problem right now is making sure new applications are aware (and make smart use of) multiple processors/cores. Even the cheapest systems on the market are dual core now, and high-end quad core machines are very common as well.
It is hard to add this retroactively though. For instance, Mozilla is working on a multi-core Firefox, but it is akin to basically re-writting the whole browser.
Also, moving to SSD over traditional HDD will get you much better random seek times, and as such much better performance for large programs that load many resources.
Last edited by MS3FGX; 01-19-2010 at 09:10 AM.