Bad idea. Bad idea. Leave it in gear if you want, but do it as a back up to supplement the hand brake. Always put the handbrake on when you are parking, for sure.
I think i read something in my ford handbook thingy that said if u are leaving ur car for a long period, (im guessing they mean months rather than days though) that u should release the handbreak, this sounded pretty bizarre 2 me though, what do u reckon?