I've seen and used them before Prince. I think they are a great idea... and can make some serious revenue... given that you find excellent places to locate them. If you find a hot spot to locate them then you can make some good money. Place them in a dud location and you're screwed. Well, only screwed so much... since you'll own the machine itself, you could move it to another location if one was bust.
However, I've used them and spent a good bit of money on them when I was away from home and couldnt find an internet connection.