1. with apple products you also have the option to make the devices not sync with your itunes. this is great if you have more music than space on some of your devices.
2. amazon has a downloader [and an uploader for that matter] so that if you do go with itunes, the downloader will convert anything you get from amazon into itunes format [or whatever other program you might be using].
most formats are compatible or easily convertible anyways, so long as your buying them from retailers and not downloading from sharing sites.
3. i'm just going to say i love my ipod nano. it has music, radio, and nike plus [and you don't need the little shoe sensor thingy for the nike plus]. the pedometer is great and it doesn't clack. and while the mileage varies as reported [my nano says 1.3 miles while mapping it out says 1.8 miles], you can actually calibrate it to your pace without the extra shoe sensor [i just started running without calibrating it, realized it was wrong, figured out how much it was off by and go by that since i don't want to lose all my old data. also, since it thinks i go not as far as i do, if i strive to hit my goals on the skewed nano tracking it means i'm actually going much faster than my goal. for example, i need to be able to hit a 16 min mile for my half marathon this fall. if the nano is telling me i am doing it as i am doing it, i'm actually ending up making a 13 min mile. and i am so used to it being skewed i don't want to think i can slack off]. and it's tiny and clips to clothes.