I don't use Vista (or XP)
However, what we have heard from trouble tickets:
Email breaks in fun and interesting ways -- the new security requires juggling back and forth between the admin and user account to get things working properly. Annoying, but, easy to workaround after reading a few knowledge base articles. This was due to filtering port 25 at their ISP, and adding an alternate port to the firewall to allow a connection. Some broadband providers still allow port 25.
Photoshop and dreamweaver both have patches available that you can download to make them work. Itunes breaks, as well as adobe's pdf viewer. I've heard flash breaks, but, again, an upgrade fixes it. I don't believe there is a fix for itunes yet (but, they have published a workaround)
there are patches, fixes and workarounds for all of the issues if you have the time to look around.
These are all issues encountered during an upgrade. Make sure you have plenty of ram -- 2gb is what we've seen as a workable minimum.
If it were me, I would wait 30-45 days if this is a machine that you are going to depend on as an income producing machine (i.e. graphics, renderings, photo touchups etc). Let the paying Alpha testers shake out the bugs first.
Also, make sure you get a machine that is Vista Premium Ready rather than Vista Capable. My understanding is that Capable doesn't allow you to use the Aero interface because the Video Card or other hardware isn't able to work with the heavy requirements for the interface.
(I won't mention what my current thinking is for my next machine
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