I've lived with various other people for the last four years (admittedly in a house rather than a flat), and have enjoyed every minute of it. It certainly depends on the people you share with, at the moment I live with two other guys, both of whom are very laidback and similar to me so we have a great time, it's sort of like Joey and Chandler's house all the time here! We also each do our fair share of cleaning, tidying etc each, so there's no problems whatsoever. I can imagine it would be a bit of a nightmare if you didn't see eye to eye with your flatmate, though.