My top tip when i had to do it would be thumbtack a sheet of cardboard on the wall your bike leans against. It'll stop you making marks on the walls or taking chunks out them.

My other top tip would be not to fumble with a chaintool causing a very manky chain to fall off the bike onto the carpet…

At uni I had at least one bike in my study bedroom. First year it lived in a bike bag with wheels off, I used to clean it in the kitchen. Initially my housemates copmplained then they realised that the only time the kitchen ever got cleaned was when I swept all the rice, pasta and fag ends off the floor at the same time as sweeping all the mud up! 😉
2nd year I had a huge room so no probs there but in my final year I had the MTB propped vertically at the end of the bed and held there by a toestrap around the front wheel and waterpipe! The road bike lived under the desk, wheels off, it fitted perfectly! 🙂

There's always ways round it and so long as you're careful with cleaning and storing them there shouldn't be a problem.