I've played with the UX-50 at the store. The first time I saw one I was definitely awed by the size and the packaging. My first complaint as a Zaurus user would be the small screen and the quality of the display. The C860 screen smokes the Sony. I'll give Sony high marks for getting wifi and bluetooth into such a small package -- in fact, I'll throw stones at Sharp for being near incapable of packing as much good stuff into a larger package. Sony get high marks for the cool docking station and the connector for carrying the UX-50. Sharp get high marks for SD and CF slots. Sony get graded way down for memory stick (that's also why I've dropped Sony cameras).
Sharp get huge marks for using Linux. I love having a real portable computer with a shell, SSH, X and all the free/open source applications out there. There are a ton of good Palm apps (I used to use a Palm V -- the nee plus of Palm branded PDAs) out there but most of them are shareware and closed source. I like knowing that I can usually recompile or find an IPK someone else has compiled and just use it. That's the power of free software.
As for video playback, I've never tried it but hope to soon. I'd guess the larger 480x640 screen and the Sharp CG Silicon technology would be way better than the Sony. I suppose for some users the built-in camera in the Sony is the plus and they should get some credit for it.
Lastly, I won't outright agree with the numerous ZUG users who say the Zaurus isn't a first choice for PDA/PIM use. I personally find the Sharp PIM applications work great for my needs and have had no trouble with syncing both with a 5600 and 6000 -- my short experiment with a C860 was a little less encouraging as far as syncing goes but I sold it for other reasons. (My only complaint is the inability to snooze an alarm -- a problem the original Palm also had). As a "pure-play" PDA you
might find the Sony a bit more compatible (especially if you're a Mac user) but I won't concede any significant lead to Sony/Palm on this point.
See this
review of the 860 over at PDA Buyers Guide -- they have a few comments comparing the 860 to the UX-50.
Good luck and I hope you enjoy your new portable!
--Aaron
P.S. I should add that in terms of pure sex appeal the Cxxx series can't be topped! To make it a perfect PDA just add wifi, USB host ability and use the screen from the 6000. Throw in bluetooth and wow -- sell me one ASAP!