One of my readers tipped me off to an interesting interview with Noel Borthwick, CTO of Cakewalk.  He talks about the improvements made in Vista for lower-latency audio via the WaveRT driver model it introduced.  To date, support for this mode among non-motherboard-audio has been slow to develop.  Most motherboard audio parts support it.  Those who are using it with the supporting parts are finding success.  He also talks about MMCSS which is the mechanism by which Windows gives priority to audio applications to avoid glitching, midi, and general Vista issues (UAC, graphics drivers, etc.).  Some thing are going well, others are still pain points.  An interesting read.