Everyone wants to use your tablet? Until they become as ubiquitous as our personal communication devices (unlikely) they're going to be a novelty for many and that "many" are going to want to play around with them.
Lock screens are pretty pointless in that regard ... enter App Lock! Thank you and you're welcome. This app allows you to apply a lock screen on an app-by-app basis freeing me to unbegrudgingly hand my HP TouchPad loaded with CyanogenMod 9 v0.6a over to whomever asks without worrying about them getting into my financial app, e-mail, Facebook or anything else I choose.
I have it on my phone too but I don't often get asked to hand over my phone for someone else's entertainment. I would love to have unique user profiles accompanied by a login and password, but until then this app should fit the bill.