It's pretty good, although with the Sony headphones plugged in the battery life ain't all that...this is probably because instead of letting it play the songs in order off the hard drive I'm usually shuffling the tunes and cranking the volume so I can drown out the assholes on the LRT who think the world is their phone booth. Most folks seem to get from 10 to the recommended 20 hours out of the battery, and in my case I probably won't be listening to it for more than 3-4 hours at a pop anyway. (See the discussion on Omar Shahine's blog comparing the Carbon to the iPod mini and iPod 4GB.)
Fortunately, the dual-purpose charger/USB cord is similar to the HotSync cable for the Palm, so if I ever manage to forget the charger I can always take a break from the Carbon and plug it into the workstation to recharge. Unfortunately, when it's plugged into the workstation I can't listen to it, which is kind of odd, but there you are. I suppose I could listen to individual albums by using Windows Media Player 7, but that's a pain.
Loading the music was pretty simple - I opened up the Rio Music Manager software, picked out the music on Cowzilla's hard drive that I wanted to port to the Carbon, and a few minutes later it was all done. Ripping music is still easier with WMP10. I can't speak to how well the Carbon works with M$FT's new Plays For Sure service, which the Rioware automatically updated to accept the last time I was adding music to the Carbon, and don't plan on finding out for a while since the cash flow is extremely sucky at the moment.
The user interface - if it was any simpler it would be too stupid. It's very easy to play music by genre, album, artist, playlist or individual song, and very easy to set up playlists using the Rio Music Manager. The controls are easy to operate and not overly sensitive, so if you tuck it in your pocket you don't have to worry too much about it skipping a track or stopping on you. The Carbon was also designed to be shock-resistant, so if you were so inclined you could go jogging with it.
Unfortunately all the cool kids in the media were mesmerized by Steve Job's Jedi mind trick abilities and completely ignored the Carbon despite its good review on C|Net. Rio Audio went under last year, so there's no new Carbons to be had. The remaining stock of factory refurbs is being liquidated through S2G, and you can also buy them through Amazon but at the MSRP. Worth buying, until Palm comes out with a hard-drive and WiFi-equipped Treo, which would be a great replacement for Palms, Carbons and cellphones alike. Not that I expect to see anything like that soon, unfortunately.