I'm looking into buying a 64GB 11" air, and I own a 500GB Seagate external drive. I don't need to bring my entire collection of music/movies/pictures with me to class every day, and keeping all of that on an external drive would free up about 50 GB. I haven't used the drive for anything aside from Time Machine backups (on a 200GB partition) so far. Other than being tied to the desk (the HDD has its own plug, so I likely won't take it with me), is there any disadvantage to keeping data on an external drive? Will there be any slowdown or strange behavior because the computer is accessing it through the USB port? If I keep iTunes and some or all of its info on the external, will it cause any issues with backing up my iPhone? What will happen if the computer tries to access a file that's on the external drive, but I'm away from my desk?