I recently installed a fresh copy of 3.3.2 on my server and the "Add New" has gone missing for Plugins. I did several searches and didn't see that this had already been listed as a bug. Perhaps it has simply been moved around and I didn't catch it in the release notes.
I changed permissions on the Plugins directory and all the usual tips. I have deactivated and activated existing plugins. Deleted plugins. I can manually add plugins with success.
I have uploaded and overwritten the existing plugin directory with one from a 3.3.1 build which did not present this problem.