I have played a few over the years, and they are a great way to proceed onto bigger MTT games at a low price. Recently on Pokerstars they had a free-roll that paid the top 100 an $11.00 buy-in ticket, to a Sunday million Final, and there were over 12,000 entrants in the free-roll and I finished 52nd, winning the top ticket.
I was also in a satellite, that gave you access to another satellite game and the top 5 would play a televised game against 5 top professiol players, but unfortunately was held up at work and missed the first hour of the game and was down to 15 BBs when I got home.
Still it cost me nothing but a little time I spent playing and that has never bothered me, Satellites are worth playing especially the free-rolls, and even some of the micro stake buy-ins can reap big rewards if you make the money in the final, it is all down to time spent playing and if you consider that to be important to you then give them a miss, but if you have time to spare, Go for it, nothing ventured, nothing gained.
When the fun Stops, STOP!