I just got my clipless pedals a little over a week ago and after riding them for all that time I took my MTB out to the local BMX track yesterday for one purpose only, to learn how to unclip in a hurry when bailing. I am just getting in to trail riding and I would much rather fall on some semi-soft dirt at the BMX track and get a scrape or two then I would on a big, hard rock or tree. I took a few little spills and as it turns out I unclipped just fine when going down. I think I will be somewhat okay when I hit the trails a bit harder.

Practicing riding around and knowing when you are about to unclip does not work for when you are in a "hurry up and bail" situation (in my opinion). If you decide to get them, ride around with them for a few days and when you feel comfortable take several practice laps at your local track.