When Vista launched, I bought a mid-range XP machine a month before. It came with a free upgrade to vista. I chose to hold off on upgrading having experienced Win 98 and Win ME launches.
My office also replaced my work machine 3 months later with a new cheap vista machine.
The work machine was an absolute disaster. Random crashes, slow, and driver incompatibilities for the first 3 months. After the first service pack and I convinced our IT to upgrade the RAM it stabilized and started working well
Once SP2 rolled out, I upgraded my home machine. I had zero issues with it. It worked seamlessly.