Getting around Cancun is so easy that even during spring break, the party-goers never fail to find their way back to their hotel rooms!
The bus service in Cancun is excellent (if not a little fast!) as they are frequent and cheap. A ride from the hotel zone to anywhere else on the bus route will currently cost you 6.5 pesos (approximately 65 US cents or 40 UK pence!) and they run all day and night long, if you miss one then don't panic - another will be along in a minute!