I've had an Etowah Outfitters tarp for years. I like it, but I don't tend to use it a lot. It packs into its own pocket, fits in a backpack nicely, and weighs less than a pound, so it gets brought along often as a "just in case" option. Usually turns out to be worth it if a storm blows through.
I have a SL5 tent that's not much heavier than a tarp, and just works better for sleeping under, especially in storms, blowing rain, or snow.
My cousin has a Cooke Custom Sewing tarp. It's a larger (largest?) size, 10x14' I think. We use that all the time on group trips for storing gear in camp, cooking and sitting under.
One thing about UL silnylon, it doesn't block heat from the sun at all. Leaving your gear under one of these tarps is the same as leaving it out in the sun. Not nice for afternoon naps, either.