I've got a 5G 60GB, and like it. No, you can't pull songs directly off the ipod to a PC; that's a bone Apple threw the RiAA so they couldn't be accused of enabling mass transfer of mp3s. If you buy something from the itunes music store, it is DRMed; but buying stuff from itunes music store is not necessary to use the ipod, and an ipod is not necessary to buy stuff from itunes music store.
I use and like itunes, I think it's a good library management tool, and I love smart playlists. You can actually pull the songs off, but they're named in Apple's wacky format "xtra.mp3" or something. Of course, you can download free software to put on your ipod to translate that, so it could still be done.
The higher the bit rate, the larger the file, and the more the device [any device] will have to access the HD, and the harder the processor will have to work to process the song; so, the less the battery will last.
Cost: When I researched, the 60GB ipod was the cheapest per-gig; the creative video was the most expensive. You could obviously save money buying a previous generation, or refurbed, of course.
I am currently storing 1.5 GB of work backup on my ipod, having spent three seconds turning on an option in itunes, and about sixty seconds transferring over USb 2.0. So you certainly can use it as a usb drive, very easily.
I will fully admit that certain other players have some additional features. However, none of them matter to me. FM radio? I haven't listened to FM radio in years, and don't plan to start now. Besides, I just bought an mp3 player/voice recorder with a built in FM tuner for 15 bucks [bought for the voice recorder], and I've got at least three little FM radios I got for free that i could use if I really needed FM. I'll admit that's a feature to some people, but I will also admit I can't understand why.
Formats - yes, other players can play additional formats. Again, depends on the consumer. I have 12000 mp3s. I'm not going to convert them all to ogg or aac or whatever, and I don't buy anything but CDs or Mp3.
The Zen Vision looked 'toylike' to me, and didn't feel too great in my hand when I tested it at the store.
Luckily, of course, there's lots of competition out there; the only bad thing is Apple's Microsoft-ian tactics in selling aac on itms and not letting anyone else have the codecs.