Okay, so I am not the fastest news source on the block. Here it is anyway. OS 10.5.7 is out as you probably know from every other Apple news source including your upgrade icon bouncing around in the dock. What you may not have heard is there are reports coming in from all over the place on the effects of upgrading.
Of course the reports of "hey I upgraded and everything broke" are out there as usual. That is not what is interesting. What is interesting is that numerous sources are reporting that there are performance gains everywhere from mild to drastic. What's more is that there are some people claiming that Aperture positively rocks after the upgrade with no other changes. I have heard this from a couple of sources and it seems to correlate well with non-Aperture users reporting improvements in various graphics and streaming video related activities.
My own upgrade seems to have produced a mild dose of additional snappiness, your milage may vary. By my cound about 1000 fellow Aperture users visit the site per day at the moment so if you have any reports related to Aperture performance post 10.5.7 I am sure others would be interested in what you see - comment away with your experience - good, bad, or indifferent.