No official changelog yet, but Ableton has released a 6.0.5 update to Live. (See latest versions to download, provided you’re registered.) This version appears to resolve some of the bigger issues with Vista. Given good experience from some users with SONAR and FL Studio 7 and audio drivers, that could make it worth trying out Live on Vista on a second partition or second machine, even if it’s earlier to make the full switch. Thanks to everyone who pointed this out.