I have the Plantronics 590A set - owned them for just over 3 weeks now. I have a couple of concerns with them:
1) They aren't overly comfortable. I broke down and modded my set by replacing the foam earpads with padded ear cushions I removed from a set of JVC HA-B25-SL headphones. Plantronics makes some padded ear cushions but tech support couldn't tell me if they would fit the 590s. When I saw the JVC set were the same size, I bought a pair to cannibalize just for the ear cushions. The Plantronics ear cushions are these:
http://www.ahernstore.com/19025-01.html
2) The LED ring on the right side is very annoying in a darkened room. It flashes continuously while they're on, and they are quite bright. It can be annoying to people on your right, like the passenger beside you on the bus. I'm planning to remedy this issue with a little silver nail polish or model paint, leaving just a small portion of the LED ring visible for notification.
3) As expected, they don't currently work with the Axim X51v. I'm hoping that Dell did implement A2DP and AVRCP in the next ROM update (A08?). I use the BT tx that ships with the 590s and the sound quality is great - it also has very good range.
Things I like about the 590s: the sound quality before I modded them with the ear cushions was acceptable, but with the cushions they're even better - they isolate outside sound more and create a bit of a chamber providing better bass response. I also really like the fact that they are both BT stereo headphones AND a headset - the built-in voice tube system that Plantronics uses actually has pretty decent quality sound. The 'flight cable' for using them hardwired on an airplane doesn't use the battery at all, and they work quite well with the BT dongle on my PC at home. Combine that with the home charger and the USB charging cable and it's quite a well thought out kit - all accesories included.
Some reviews:
http://www.mobilemag.com/content/100/335/C5517/
http://www.thinkcomputers.org/index....reviews&id=349
Note: the reviewer at Thinkcomputers states he was able to use his 590s with Skype, but as of yet I haven't managed to get the voicetube microphone on them to work with my PC. It works beautifully with my Jabra A210 universal BT adapter (for non-BT phones) and with a friend's Nokia cellphone, so I know the voicetube microphone works. I suspect it's a peculiarity with my USB BT dongle and the BlueSoleil stack it comes with. I'm planning on getting a new Class 1 dongle with BT 2.0+EDR support, hopefully with the Widcomm stack.
Let me know if you have questions.