Recently the city began a night bus that does loops through all of the city's hot spots on Fridays and Saturdays. It runs till 3 am and costs $3 for a ride-all-night pass. The city uses the regular daytime buses (which are very nice) and loops around every 20 minutes or so. The bus runs through downtown, the Strip District (clubs & bars), Station Square (Hard Rock, restaurants, comedy clubs & a few bars), South Side/ Carson Street (trendy bars, coffee houses & restaurants), Shady Side (upscale cafes and shops) and through the colleges. It's a wonderful idea if you want to drink but don't want to worry about having a driver or taking a taxi.
For more info: http://www.ridegold.com/ride/pgUV.asp