Initially I had the same problem, the uploader wouldn’t work, however after changing permissions (775) the situation appeared to resolve itself.
The directory wp-content/uploads was *not* auto created, but apart from that, I honestly can’t say I observed the same symptoms as reported here. As far as I can see, ownership and permissions appeared to be the issues to resolve, and once that was done, everything else worked just fine.
Environment: ubuntu 7.10/Firefox 2.x and uploading to WP hosted on Plesk 8.2 running over CentOS.
