The industry makes an effort to create and adhere to "compatibility" standards, like PCI, ATX, DDR, AGP. They also make an effort to change those standards when the changes promise some boost in performance.
It is times like these that I hang back, read all the computer-tech news I can, investigate who's selling what and for how much, and focus on tuning up the equipment I have.
This year promises to be "volatile" in techno-change. You have AMD and Intel promising dual-core processors; you have AMD hanging back on DDR2 while Intel is jumping in head first; you have OCZ spearheading improvements in DDR2, but I don't think that technology will be mature for another year. And you have companies stumbling to produce "SLI" compatible motherboards -- check the ASUS home-page, for example.