Some (but not all) people who have gotten their hands on Oblivion already have complained about long load times. How long, you ask? How about ten whole minutes just for the inital load! Someone from Bethesda made a post on the official Elder Scrolls forum that solves the problem. When you first turn on your Xbox 360 hold down the A button while Oblivion loads. This clears the hard drive cache and lets Oblivion start fresh. Don't worry, you won't lose any game saves or anything. The hard drive cache allows for faster load times by copying and reusing some data to the hard drive, but sometimes the data in the cache can get fragmented which results in slower data access.
The results of using this handy trick? Gamers have reported initial load times as quickly as 45 seconds and then the rest of the game (menus, dialogue, etc.) loads very quickly. I hope this helps some people.
The Elder Scrolls Forums -> Xbox 360 Long Pauses with Hard Drive