Personally, I don't own one, but have borrowed HC's "Neo" tarp a couple times and found that it provided suficient coverage. I used it on my now infamously ill-fated AT section hike and had no problems with it at all. I had a pretty heavy rain the night I was out and stayed dry as a bone, even after I wound up on the ground sleeping on a root.
I also used it a night at the April SEHHA Hangout one night as well. It rained a bit that night and kept dry. It is a little heavier then most other tarps, but it is a cheap way to go for those of us who are "budget impaired".