I just downloaded the latest build of Flock, and went to configure my blog for posting. But Flock's handy dandy blog account configurator was hanging while trying to communicate with my WP 2.0 blog. A quick peek at the Flock forums revealed this is a known bug, but no fix was offered.
But... you can trick Flock into letting you manually configure a blog. When adding the account, just give a bogus URL (or, in my case, I tried to configure it with my http://.../server.php file directly. That will fail, and bring up a dialog asking if you want to try again, or cancel and manually configure. Click "Cancel" to continue (of course - I love intuitive dialog boxes...)
You are then given the ability to configure from scratch. I selected the MovableType API, blog id of 1, and provided the full url to my xmlrpc.php file as the access point. Provide your login credentials, and you should be off and running.
The category selector is a bit awkward for me - I'm used to just entering tags as if I'm tagging in del.icio.us, but Flock provides an apparently randomized list of my 200+ categories for me to check off...
If you can read this, that means the config worked, and Flock is now posting to my blog. If you can't read this, I just had an exercise in typing Dvorak, which would have been filed into /dev/null...