Ben Rudolph posted on his blog site recently that people have been asking about Mac Pro compatbility, and so he wanted to address the question as best he could.  He writes:

1) Is Parallels Desktop compatible with the new Mac Pro tower?
Not yet. The new Mac Pros have a different CPU model, and work with a specifically optimized OS X kernel. It is not difficult to make Parallels compatible with either of these, but it does take a bit of time. We should have a compatible build very soon.

2) "Very soon" sounds like marketing-ese for "we'll have something someday."
When I say very soon, I mean very soon. Like within the next few days.

3) How will we find out when the build is ready?
If you're signed up to receive Parallels news, you'll get an email from us with instructions on how and where to get the build. Not signed up? Just enter your email address on the main Parallels home page and you'll be good to go.

Ben notes that the Mac Pro was only announced earlier this month.  And within 24 hours of the announcement, the Parallels team was hard at work to get Mac Pro compatibility done.  These guys seem to work at record speeds... give them some time and they will get it out the door as quickly as possible.