Aperture has been functioning pretty well on my early 2008 8 Core Mac Pro, but I have had a few quirky items here and there. Like when I migrated a library from a MacBook to the desktop, some of the files were relabeled with the captions that I had produced for the Facebook Aperture uploader, or when I retouched in PS CS4, sometimes the new preview wouldn't re-render in the thumbnail view (although it did the large view) until one of the adjustment sliders was moved. I was happy to see the update, the number of issues addressed and the speed at which it was issued. It's 32 MBs and is available when you hit the software update or you can get it directly from the support site linked above.
UPDATE: after using Aperture for awhile after the update, my initial observation is that it is much faster / super quick to bring up any given screen (even full sheets of seemingly instantaneously rendered photos in the browser view). This much more like the zippy experience I recall from Aperture 2 (which I used awhile back, although I continued with LR2 b/c of non-destructive local adjustments).