Did you buy your Mac before 2006? The chances are you have a PowerPC processor inside. And while your computer may still work fine, Adobe isn't going to serve your type in these parts anymore.
On Wednesday, Adobe announced that the next release of Creative Suites will not support PowerPC. PowerPC Lightroom users held their breath for a moment thinking they might be exempt... but no! Lightroom is following suite.
But surely, you say, CS5 must be a long way out. I mean it was only a year ago that they released CS4. Adobe's response is essentially: we are telling you now so you don't whine at us later.
So maybe by the time CS5 and LR3 come out, you're PowerPC will have lost its luster. Plus, buying a new mac is like christmas, your birthday and your first kiss all rolled into one. (Can you tell I'm a Mac devotee?) And, it looks like there is some great new stuff on the way, like the Macbook tablet and an ipod nano with a camera in it.