my take on a fast-changing situation:
aperature & lightroom -- main strength is ability to manage RAW files, and converted files. old way: RAW & each separate conversion counts as a separate image, eats disk space, slow to work with, hard to keep track of. A & L -- each conversion only saves the instructions on how to convert (exposure, color balance, B/W conversion, etc...), and you can group derivatives of the same image and handle all together.
aperature is in a troubled spot in development, and may or may not survive in the marketplace. current versions use a non-relational database, so you can't split file locations (say, some on one hard drive and some on another), you can't move files to other computers & track them, etc....
lightroom is way ahead as a database program. it's as good as cumulus, which is a pure database without image management options. lightroom has the basic RAW options (exposure/color balance/sharpening) and also tilt/crop and very good slideshow/title management.
iPhoto is catching up -- version 6 has some RAW management abilities. doesn't have versioning, doesn't allow you to group images. but not bad as a holding option until the marketplace shakes out.
photoshop is not a database program. it's value is in advanced image editing (clone stamp, layer masks, smoothing wrinkles, that sort of thing).
with the new intel-macs, none of the big-three programs will run native.
My advice: get the new mac, but wait on the expensive software. Use iPhoto and gimp until native x86 versions come out. If aperature improves its database operations, consider it, otherwise go with lightroom. stick with gimp until you need full photoshop.
iPhoto is catching up -- version 6 has some RAW management abilities. doesn't have versioning, doesn't allow you to group images. but not bad as a holding option until the marketplace shakes out.
Gimp is free, and has most of the image enditing of photoshop (lacks layer adjustments and some esoterica), but is very serviceable. with google you can find a build for the intel mac. you also need an x-windows client, which is also freeware.
the macs are great. the software will soon catch up to the new hardware, and you'll be in computer heaven.