Hi Dan
You could also have titled this 'JVC Black Screen of Death' !
I got a new JVC GR-DF470 for Christmas and it only lasted 5 days before the black screen of death, the camera displays 'LENS CAP' even though it is off.
The problem I believe is the CDD, which is actually a Sony CCD, hence both JVC and Sony cams can be affected by this dodgy CCD, not sure about any other manufacturers. If you search on Google for 'JVC Lens Cap Error' you'll find other people talking about this problem. On the JVC website they have acknowledged the problem and will repair any affected cams free of charge even if out of warranty (just need a recipt). The affected cameras they list does not actually include mine which was a 2005 model, most of those listed are older models, hence I thought I was going to be safe getting the DF470, but that was not the case
Thankfully I'm exchanging mine for a new Canon model now, didn't fancy a repair or a direct replacement as I would just worry about it happening again.
At the end of the day it's probably only a few % affected which is why JVC are probably still selling cams with this CCD - the notice on their site indicates a willingness to repair cams up until October 2007 so it looks like they know there's loads out there waiting to break down!
Good luck shopping