Apple released the 10.5.3 update Wednesday, and I decided to be an early adaptor.
On the iMac the download (420MB) took four minutes (fast Cox internet connection and Ethernet-connect to my Time Capsule). The install took maybe eight minutes on top of that, and then the system needed a reboot.
At first I got the spinning gear for a couple minutes, and then the system rebooted again. After another couple minutes I got the login screen.
Logging in, it took a while for Mail to show my mail boxes. I then performed a .Mac Sync, and also an iPhone and iPod sync with iTunes to make sure it all worked well. I also performed a Time Machine Backup Now (it needed to backup 1.5GB!).
All in all it went very smoothly and quickly.
On my MacBook the biggest difference is that the 420MB download took 20 minutes (connected to Time Capsule via wireless). The actual install took maybe 10 minutes, then the dual reboot and all was well.
In Windows I never update this quickly; experience has taught me to wait. In fact, my Windows XP boxes are still not on SP3. But in the Mac world I’m not usually worried about upgrades, even large ones like this one.