This plugin saved my life.

I've created an incredible bloated multisite network with over 300 plugins of which 70 are activated on each blog to start. The frontend of each website loads great due to caching, but the backend is so bloated that it inevitably slows down as more plugins are activated.

This plugin allows me to only activate the plugins that are needed on each admin page, meaning I can greatly speed up the backed of my multisite install, completely changing my business and my life in the process.