I'm working on a bot that will update WP plugins.
You can also use the Moverz Tuel to help with this. Create a "main" blog where you upload all your plugins. Then just have Moverz check this folder and copy and move any plugins to all your other WP installs (that you can FTP to).
Then run the WP update bot every once in a while.
It's actually a pretty easy bot, I'm just stuck on one part that's holding me up (as usual).
But this will be a great time saver for those that use multiple WP installs and what to keep their plugins up to date.