We've used Fairy Godmothers a few times at Disney, and it worked out fine. I rarely left my kids with sitters when they were younger. When they were very young, I was always nervous as to whether the sitter would be able to accomodate their routines such that they felt comfortable. I think much of it was that I also felt guilty....although I was able to take a good amount of time off when each was born, they've been in day care a lot as I have a full-time demanding job, and I had my own hang-ups about spending whatever freetime I did have with them. If I had to do it over again though, I would have done it differently. As I've gotten older, I realize, it really is in all of our best interest for DH and I to have some time together, and of course, it gets easier as the kids get older too. I think they like some time away from us as well!
We used Fairy Godmothers and had good experiences....I didn't worry too much about safety issues....I checked out the Org on this chain, and they have very good references.....I never saw anything bad about them. Additionally, my kids are older now.....last time we used them, the kids were 11, 7, and 5. I don't think the kids had as much fun with the Fairy Godmother babysitters as they have with our teenage sitters at home. I got the sense that they didn't really play with the kids that much, but they did have a suitcase of "prizes" that the kids got to choose from for being good. I thought that was kind of funny....I think it's just a basic expectation that kids should be good and it shouldn't be something they are bribed for.....but who cares, it was a few hours.....they were safe, and DH and I had a nice time.
Sometimes I think in an effort to live up to our own high expectation of what a "good mom" is, we neglect other aspects of our lives. Of course, the safety of our children is priority number one, but as long as you're comfortable about that, I'd encourage you to go for it!