So I have been using Vista SP1 for a month now and have yet to run into any major issues. I get the impression memory usage has been slightly improved, but apart from that I did not notice any improvements or degradations. Same old Vista to me. :)
One minor issue I ran into: My IPaq failed to get recognized. This manifested itself when I woke up the PC from standby mode. The screen came up, the cursor was blinking, but the mouse and keyboard were unresponsive for over a minute. THAT had never happened before. As a matter of fact, it seems that my keyboard is recognized quicker when waking up from standby with SP1. I should have taken hard measurements, before & after, too late now! But I digress, back to the main issue... Once my peripherals were finally online I noticed synchronization with my IPaq was not happening anymore, even worse, there was no IPaq! Removing and reinserting it in the cradle did not help either. Performing a soft-reset on the IPaq fixed the issue and it has not occurred since.