WordPress removes the Update Services ability when you create a network. Activate this plugin to get it back.
For some reason WordPress removes the Update Services ability (under Settings - Writing) when you create a network (aka enables WordPress MU/Multisite). Activate this plugin to get it back.
Note: This is only for WordPress setups with a network, aka multiple sites, aka multisites, aka WPMU in WordPress 3.
This plugin might work with older WordPress MU sites to. I haven't tested it though. If you do, please let me know how it turned out.