Am I in 325 or 352? It's so easy to forget, especially if you've been staying at different places each night. And most people probably won't mistake you for room service.
When you arrive at your room for the first time, take out your digital camera (or better yet, phone) and snap a photo of the room number. There's nothing more embarrassing than popping into the wrong room, especially if you're pooped or jet-lagged just to give a few examples.
Worst case scenario, you can always go downstairs and ask the front desk. But the first floor is always so far...
