I installed the update on my MacBook a little while ago without incident. It was a 136MB download through software update on my Intel MacBook. It’s also available a a standalone download from the Apple download page. The MacBook had already installed the iTunes 8, QuickTime and FronRow updates.
At this point I haven’t installed OS X 10.5.5 on any other Macs yet. I’ll wait and see what problems are reported and probably catch up with the updates this coming weekend.