I'll chip in here for the benefit of anyone else considering going down the VPS path, as its great for WPMU. My exp is based on Rimuhosting (rimuhosting.com), who provide excellent VPS plans very well suited for WPMU. MT seem to have a less technical user base than rimuhosting (for MT, using ssh and the Linux command line is considered a power user, whereas with rimu its pretty standard). Check out the rimu How To articles from their site and you will quickly get a feel for their approach.
ssh access lets you do anything you want, although if you prefer a UI webmin comes free, and Plesk is bundled with higher end plans.
Rimuhosting's DNS utility gives you full control over A records, so its easy to do your own wildcards. Or you can follow their how to and install Bind to run your own DNS. I haven't used the MT DNS utility, just scanned their FAQs, perhaps just check you can do your own wildcarding, it will be better that way for wpmu. svn isn't pre-installed, however rimu will install for you on request and setup so you can get wpmu nightlies.
If you are developing with wpmu and want to work on a small scale or with low traffic sites, wpmu works very well on a VPS with just 160Mb of memory. Will deliver around 3 req/sec on an apache bench test with 10 conc users. This is available from rimuhosting for $30/mth. That is $20 less than MT's entry level, although they work out about the same for equiv memory as you add memory and move up towards dedicated. One of the good things about a VPS is you can migrate to a dedicated server by copying the VPS image onto its own server (there is a small performance overhead involved, but the flexibility is significant). So no problem with MT, but I figured its worth pointing out the lower entry point for those wanting to make the jump to a VPS.
The support team at rimu is responsive and knowledgeable. I've been with them for coming up to a year, and had no problems with reliability or performance.