I just read this really useful tip in my 360 mag.
apprently obliv uses the hd extensivly to cache game data. sometimes the data can get overly fragmented, causing long load times, pop up, slow down et cetra et cetra. To fix this reset the xbox and hold down the a buttonas the game is booting up. once you see the bethseda softworks logo video the games loaded and the cache should be cleared meaning quicker load times.
I tried this and it worked for me so i thought i'd share the knowledge