Touristic Buses can be very easy to use and usually affordable but when I look at people riding one, they look so sad and bored... Never noticed? Do it the next time you see one.
I understand that most tourists that use it only have 2 or 3 days to see as much as possible the city, this way is quick and you don't get tired, just sit your butt, look around, take pictures and listen the guide person (if there's one or if it's not a tape). But do you actually feel the vibe of the city?
I only used one touristic bus in Toronto and I think it was the first and last time. Even if I only have 6 hours in a city! I rather use my feet and explore as much as I can. In the way I'll go to a local restaurant and order traditional food with a refreshing local drink.
The good thing about it? You can get a free map and follow the route walking or cycling ;)