I have been clipless for two years and will never, ever go back! I tell everyone I know to get the clipless pedals, for several reasons:
1. As previously stated in this thread, more power on each stroke
2. Safer. I've twisted my ankle trying to get out of toe clips, but never (once I got used to them) had trouble getting out of clipless.
3. You don't have to keep flipping them up with your feet if you're trying to get started, which, if you've ever experienced it, is so annoying! Plus, if you just leave them down they can get caught on rocks/branches etc.
4. Instant added technical skills!!! It's easy to cheat bunnyhopping, wheelie-ing, and throwing the back end up.
It also depends on how technical your ride is. If you never need to get out of the pedal quickly (and I know I do
) two and three don't matter so much.
Ride happy!