There are 20 save slots on the Xbox, a very restrictive limit considering the saves can not be backed up without over-priced third party hardware (at least on the PC you can move the saves to a different folder).
Almost true, if you get the latest update you can use almost any USB-memory for harddrive and store you're saves there (USB's are cheap ;)). You can also "back up" them and put them on a PC via the USB if you like, if you use the right program
