I happen to have the same exact issue and it seems the trigger is nothing specific. For example I was playing with it, opening apps using games etc then I realised it might be fixed, then went to bed, turned on my fav audiobook (been doing it for ever) and after a few minutes switching from landscape to portrait mode it crashed (brownish pixelation and fade out) and it went to recovery mode. Switched it off and on then worked for a couple of minutes and eventually showed me the recovery screen again. I got my phone on the 29/12/11 so within my rights I called up Apple and there is nothing they could do but arrange a replacement for me. I don't know if it's due to the update or the apps but anything could be a trigger. Just a faulty phone I guess. I'm stuck with it til I sell it and get a better 1....