How to better use a Mac mini as a home theater PC with a television set?
The following will work on Lion. You need Xcode as well (maybe you can copy just Quartz Debug from another machine; if not, you can remove the developer tools after following my steps).

Run Quartz Debug from /Developer/Applications/Performance Tools/, click on Window menu, then on UI Resolution, then check Enable HiDPI display modes.

Log out, log back in and go to System Preferences, Displays and choose one of the HiDPI resolutions.

This will effectively double all UI elements, including font and button sizes, menus etc. This is still work-in-progress, though, so expect glitches. Apple is working on resolution independent UI since forever, but with Lion came a new way of just doubling every pixel. The advantage is that this will work with nearly every application, whereas truly resolution independent UI would need vector graphics for every UI element.

I'm using this on a 46" LCD TV from time to time, to make accessing iTunes easier. One way to quickly switch between HiDPI and normal modes is to check "Show displays in the menu bar" (translating from german, might be labelled differently) in Displays preferences. This will add a menu extra to the menu bar with which you can quickly choose from previously used resolutions.