Steve Jobs announced at the WWDC keynote today that Apple is switching to Intel processors. MacNN
has live coverage. The bottom line is that Mac OS X for the last five years has been running on Intel, the switch is expected to be complete in two years, and Rosetta will allow PPC apps to run on Intel-based Macs, transparently. If you're using Xcode, it is small changes and a recompile; otherwise, you might be seeing a lot of work ahead of you. You will be able to order the 10.4.1 preview for Intel today.