I have one. Its a great practice tool. The "remove a guitar part" feature for the most part works really well. A few times its not quite there but more often than not you can get good results. The track it leaves behind after removing the guitar sounds a little odd sometimes but I dont tend to notice whilst Im playing.
I get a lot of use out of the detuning feature. If Im playing along to Stevie Ray Vaughan for example, I set the backing track to a semitone higher pitch, which lets me play along in standard tuning.
The amp sim/effects part of the JamVox has got some really good sounds to it. Ive not used it a lot besides the presets tbh because I have a POD X3 which I use for stuff like that.
If I didnt have the POD Id get a LOT of use from the JamVOX. As it is I only use it to play along with cds which seems a bit of a waste of £150, so Im looking at selling it. If I didnt have the POD Id never switch it off.
If you get one you may find a really awful popping/crackling noise when you try and play and there are a huge amount of posts on the Vox forum about it, but I found that as soon as Id updated the software to the latest version all the troubles disappeared.
Heres a vid I made showing some of the presets. Ignore the sucky playing, but it shows what sounds you can get right out the box.
http://www.youtube.com/watch?v=G4tNurVJClk
