I used to be a Presenter / Engineer on one for seveal years. It was good fun, and I met lots of interesting people and made useful contacts.
Don't have this vision that you will get 100's of people listening and phoning in for requests, becuase it just doesn't happen, unless you have teams of other volunteers "Request Running" around the wards and getting people to "tune" in

. Unfortunately Satellite Tele, and the introduction of Personal CD / Minidisc / MP3 players have virtually stopped Hospital Radio in its tracks

.but don't let this put you off, it is good fun and practice!.
If you are looking for a career in Broadcasting then Hospital Radio is a MUST. If you intend to work as a presenter, Tech op, Com-prod etc in radio then you need at least a few years experience on H.R to gain a good chance of getting into the industry. The same applies really for any media related occupation.
Have Fun!