I bought an Archos 6gb well over a year ago. Kinda bulky, kinda heavy, but it works well. I didn't like the original Nomad's size - way to huge. The III looks to be similar. I have yet to see and play with a Riot, though it looks cool. The IPod is awesome. Looks great, sounds great, easy to use - though I would be worried about scratching it. It's too pretty.

I used my JB 6000 extensively with a line in plug prior to buying an empeg. Afterward, I used it regularly at work. Battery life was pretty good as long as I refrained from skipping songs constantly.
Playlist size is limited to 999 tracks - and that takes a minute to load one of that size. (Winamp playlists work fine - no need to use the bundled musicmatch jukecrap)

Initially, it had some software quirks. At the time I bought it, they were releasing upgrades fairly rapidly. Now they haven't released anything new for it in a lonnnng time. It basically works as advertised - it just takes some experimenting to figure out some things (documentation is lacking). Email requests for explanations never had a response.

The JB 6000 reads ID3v1 tags only (title only). I found that removing the tags entirely, forcing it to use the filename, gave a few more characters in the scrolling display. But still, not enough characters are displayed. That sucks.

Searching for songs depends entirely on how cleverly you arranged directories.

Occasionally, when playing, a song will "blip". Not sure why. And if you bump it too hard vertically, it will also blip - but I believe that might be due to a momentary loss of battery contact.
I also purchased the accessory kit. Remote, headphones, cassette adaptor, car power adaptor. The remote works well, though it feels rather flimsy and I worry about durability. Headphones were crap. Cassette adaptor works about as expected. Power adaptor causes a lot of noise in the system, so is useful only for recharging the batteries. (note that the remote supposedly only works on the player versions - Not the recorder type)
If the fickle gods of weather send some decent snow this year, I plan on trying it out on the slopes. I found a cool over-the-shoulder bandolero-type gameboy advance case that should work well for skiing.

Overall, the unit is serviceable. And makes a great file-transfer device between computers. I do envy the nifty features of the Nomad, IPod and Riot, though. The Archos line is quite a bit cheaper than the others, but does lack their features.