Reality shows have become one of the fastest ways for old celebrities to revive their careers, introduce themselves to a new generation, or regain media interest and attention. Celebrities who went virtually unheard of for years (i.e. Corey Haim, Corey Feldman, Scott Baio, Dustin Diamond) are now in the press again...and have paychecks again. In a way, it is kind of sad that this is their only option, so they do not fade into obscurity. On another...I guess its good for them! I mean, being a has-been has got to be painfully depressing.
It is funny though that even if you take "real people" and put them on reality shows...they eventually become famous and then they are celebrities and not average people anymore! Look at the cast of The Hills, Trista and Ryan Sutter (ok, they aren't mongo celebs, but they are well-known).