I've been vegetarian for about 5 months now.
I haven't felt an increase in energy, though.
I do feel lighter. I feel that I have greater immunity to sickness (I haven't contracted any colds this season.) I also feel I can push myself hard, and work longer with less sleep without any drawbacks.
Overall, I feel healthier. Lately, I have been having cravings for meat. But I don't have the inclination to going back.
I'm definitely not as hardcore as some vegetarians, I did it primarily for the health benefits. I don't feel a greater spiritual awareness, nor a greater clarity of thought. I don't consume many animal products in general.
So I think we each take different experiences out of being vegetarian, and have different reasons for doing so. Mine are pragmatic.