I was lucky enough to see the gorillas in Rwanda last year. There is a fair amount of hiking and you need to be able to carry all your camera gear without a bag once you get close enough to see the gorillas. I used a Digital Rebel with a 70-200 f2.8 IS lens. I brought a 1.4x teleconverter for other wildlife but it was really not needed for the gorillas. Some other people used 100-400 and 70-300 lens too. The key is really to travel light and enjoy the gorillas when you do see them.
I posted a few pictures at the end of a thread about gorillas here:http://photography-on-the.net/forum/showth...ghlight=gorilla
A friend of mine went to Uganda to see gorillas a few years ago. Apparently it took a lot of work. She and her husband got an 8 hour hike the first day. The second day the guides were able to limit it to a few hours. She also commented that it was an intense hike. However like most things, your experience may be different.