I don't have a doctorate in LCD either but everything that I've read/seen has stated that they are not subject to 'burn-in' like you are mentioning. Like kbghdg mentioned, it has happened to him also but then the TV died right after. Perhaps your TV is about to die too and 'everything' is burning in but you actually only notice the guide. ...I hope that's not the case!
I replaced our DLP HDTV with a LCD. Just before the DLP died (the 3rd time) I asked the repair man what kind of HDTVs are the best in terms of quality/not-crapping-out and he said none of them... that no matter what kind you get, there's some drawback to it and he hadn't seen many HDTVs (of any type, plama, LCD, DLP, etc., anything) that lasted nearly as long as the old standard defs.