with root i can do (or did) the following:
-wifi tether,
-block advertisements,
-remove stupid apps like city ID that run in the background but don't actually do anything,
-use apps like autostarts that let me decide what apps start up when the phone boots,
-use apps like quickboot that boot me right into recovery from a single tap on the screen,
-theme and then install widgets to make them look how i want them to look,
-run a low voltage kernel to possibly help with battery life(only flashed it last night so i don't have any real results yet)
-i can make nandroid backups so if i ef something up i can always revert back to a safe and stable point
-i can connect to wireless N routers now that i did the wireless N hack
i'm sure i'm forgetting a thing or two... and there will be more things to do with root later on.