UPDATE: With the new versions of WordPress, you can install updates for themes, plugins, and core WordPress from Dashboard > Updates.
WordPress 2.9 introduced batch upgrading of third party plugins, among other features. Given that most of us tend to use a dozen plugins, which get updated more often than not, this is probably the most useful of all new features of WordPress 2.9. The problem is, how to batch-upgrade plugins?
The obvious place where you’d be expecting this tool is under “Plugins > Installed” in your dashboard. Somehow, the developers didn’t put it in there. Where you’ll find it instead is under “Tools > Upgrade”. This is the place that used to help you automatically upgrade WordPress to the latest version. Starting with 2.9, you can update third party plugins from here as well.