I upgraded a fully-working WP 2.9.2 site yesterday to 3.0.
When using the plugin manager or the themes manager in 3.0, it hangs at "Downloading install package from http://wordpress.org/extend/themes/download/blahblah.zip..." when uploading a new file.
The thing is, it actually does install the theme/plugin correctly, but does not update this screen to tell me the status so I have to guess when it's finished.
I have tried using nginx and httpd; it's the same. I have tried with php 5.1.6 and 5.3.3; it's the same. I have tried Firefox and IE8; it's the same. Server OS is Centos 5.1, MySQL 5.0.7.
I have tried installing a fresh WordPress 3.0; it's the same.
Uploading other things, such as images to the media section, works fine, and the progress bar works.
Any suggestions are greatly received!