I did the six-person-per-room thing in college too.

Bottom line is that it depends on the city and the size of the hotel. If you're going somewhere like the mgm grand in Las Vegas, they'll probably never know. If you're going to a 30-room hotel in Dublin, they probably will.

Biggest tip is to be quiet. I don't mean that you guys should whisper, but be aware that 7 people talking over each other with the television and/or radio on will probably result in one of your neighbors calling security. If that happens, you're looking at a minimum of an extra fee for each person (anywhere from $15 to 50 per night depending on the hotel) and/or being kicked out if you exceed the fire code.

Oh, also try to pick up the room a bit before housekeeping comes. Don't have 7 toothbrushes in the bathroom or 7 distinct piles of clothes on the floor (use the dresser and closet). And try not to all walk in together. Just basic stuff to avoid the staff's attention and make it less obvious how many people are staying in the room.

Good luck and look forward to the day when you can travel in a smaller group.