It has 23 security updates, 550 hotfixes, and is packed into a 434.5MB package or 726.5MB for the 64-bit version. That’s a fat service pack if I do say so myself.
Some of the more apparent fixes include file copying ETA being more accurate, UAC should pop up a bit less in certain areas, and DirectX has been fixed to support DX9, DX10, and DX10.1 hardware. They also fixed WGA to fix the two most common exploits of the system and they’ve added some more support for third party search solutions.
Prior to getting the service pack you must have, in order, updates KB947172, KB937287, and KB938371 installed, each of those may or may not have their own sets of prerequisite updates, but I’m sure you’ve got all that covered already right? What I really want to know from you, the readers, is does this new SP make Vista usable? You see I’ve had a copy of Vista Home Premium ever since it was released and I installed, and then promptly uninstalled it, shortly after I got it, but if Vista is now usable again, myself, and I am sure countless others, would be interested in knowing if its worth the update.