Software incompatibility has been a huge issue with machines running Vista, but things are getting better. Those that rely on Grisoft's anti-virus suite haven't had Vista support for the past few months, but now it has been updated to provide compatibility. This is for their Internet Security suite, and doesn't include their entire product line currently. It is available for download starting today, weighing in at 41.8MB. You can read the full press release from Grisoft in the comments section.
There are still myriads of software packages out there that do not support Vista yet, and it is causing some businesses to hold back on rolling out Vista for that very reason.