Probably Fallout: New Vegas (after buying Halo: Reach). Game looks awesome.

If you really must back up your data, you can do it using USB flash drives. One thing about transfering to a new hard drive is that after you transfer your data, if you want to play XBL arcade games and use certain DLC and other content offline, you must first transfer the content licences to the new console. You can use this guide once you are done transfering to the new Xbox 360.

I should add that you're not actually connecting the consoles directly to each other but rather connecting the cable to your existing hard drive, and the other end should go into the destination console's USB port. Of course if you have a USB flash drive, you can transfer the data that way as well.

According to this article you can use the Xbox 360 transfer cable to connect both consoles and transfer the data.

There's really no way to know this early. But knowing Microsoft, if it did fail somehow , it would be mysteriously right after the warranty has expired. I'm hoping that they would have learned from their mistake by now though.

Matchmaking alone makes this a win. Not to mention Rocket Fight, customizable match options, and the ability to create your own custom skulls.

They will most likely feature it in some way, but probably not as prominently as in this E3.