I recently wasted quite a few hours trying to find a bug in my code, and it seems that eventually the problem was some borderline behaviour when using the internal pull-up resistors.
I moved my tested circuit from LP to a home etched board and thought I'd damaged one pin as the input as it wasn't working. I hastily shorted it to another pin to salvage the board and was surprised to see BOTH now behaving. (I left out the boring and lengthy steps of spending hours blaming and debugging my code and/or a last minute switch from F2013 to G2452.)
Anyway, the end result seems to be that the internal pull-ups (G2452 in TSSOP14) don't seem to work. It's just a simple switch to GND with internal pull-up enabled. Sometimes it works, sometimes not. Adding an external 10k solves it. Perhaps I've got a partial short somewhere, but I don't think so.
Anyway, my question is this: Is relying on internal pull-ups considered bad practice? I just did it to save an unnecessary resistor on a tiny board that needs to fit into a tiny space. (Also one less chance for me to screw up the etching/soldering.)