I fired up a localhost I had here at work. Moodle 2.0 dev (Build: 20100331) last modified according to Windows explorer on 20100406. I see all the old themes with eraser marks on them. Plus Anomaly and Flower Power which I just downloaded. The button is still there at the top.
I then followed Martin's announcement about Preview 2.0 to Moodle docs and clicked on the "get it" link. and installed that over my existing Moodle. Notifications still shows Moodle 2.0 dev (Build: 20100331) but it upgraded the blocks.
On one of my home localhosts, I did not see any themes just the button and upgrading..
I will delete the entire local host at home and put up another complete install package for 2.0. Sorry for the false error reporting. Agree that it is resolved until I break it again