the fine folks at Amazon have DRM'd most, if not all, of their books, which means they're "locked" to your kindle. There are "ways" to get around this, but not that can be discussed here (google is your friend)...

I haven't had any problems with light modification of word/powerpoint files (haven't tried anything with swapping images yet though), and moving the files from the eDGe to your computer and back again is as easy as connecting a thumb drive and moving the files to it.

The internet is pretty useful - more so, I'd say, than a mobile phone since you have the option to use "desktop" mode which more often than not will pull up the full version of sites, rather than their mobile (watered down) ones. Right now video playback is the big lim-fac here, but once they get the flash support up, that should greatly improve.

Listening to music is no different than your MP3 player - you can use the built-in speakers (nothing special), head phones, or connect external speakers...soon you should be able to connect bluetooth speakers/headphones too.

HTH