I have just upgraded 1.52 to 2.0 RC3 and apparently found some problems. I'm using the latest Mozilla Firefox on MacOSX 10.3.9.
First: upgrade.php gave me errors (details here: http://jarnon.muumilaakso.org/images/wp_problem1.tiff). However, the upgrade seemed to work fine after clicking forward because upgrade.php created this missing wp_usermeta table and this table works just fine.
Second: I tried to create a new post and change the post author without luck. I have three authors in the database and wordpress showed only the "admin" one in the select menu. Check the picture to understand better what I'm talking about: http://jarnon.muumilaakso.org/images/wp_problem2.tiff
I hope this helps you. :)