I tried Aperture for 30 days about a month ago... Mid-way through the trial period i got iLife 08... I find that Aperture is a bit sluggish, even on my MBP with 3gigs of ram... The library only had about 1200 photos in it... my iPhoto 7 library has 13000++ photos, but runs extremely fast & without problems ... iPhoto 7 is a HUGE improvement over iPhoto 6, and it has most of the editing functions that you would commonly use... Link Photoshop as the external editor, and you'll still have nondestructive editing with more editing capabilities compared to Aperture...

Aperture is a powerful application designed for professionals, it helps with the workflow A LOT!! Archiving onto offline media is also much easier... It works well on dual monitor setups, but it felt cramped when I used it on the 15" notebook screen alone... It also lacked some features that I thought were quite essential, such as lens correction tools... I eventually thought that it's not worth the price, so I didn't buy the licence... I'm now using iPhoto 7 linked with Photoshop CS3 as the external editor...

Try it out before you buy... It's a good(not great) application, but it's not for everyone