Good morning David.
I'm the buddy that John mentioned in the above post and that's my green tarp that he showed a picture of. As John mentioned, I've been using it for 5+ years now and during that time it's seen 15+ days of rain or snow. In fact, during the one elk hunt in Utah, it rained solid for 5 out of the 6 days and I'm not talking an intermittent or light rain either. We're talking all-day soakers. The tarp has held up great during it all and I've never gotten wet while under it. This is especially important to me because I use a down sleeping bag. In fact, of the 4 people on the Utah trip, I stayed the driest even though the other 3 all had tents. I definitely had the most room also.
So do I recommend a good silnylon tarp? You betcha. In fact, it sounds like I have John convinced and he's leaving his tent at home and bringing a tarp when he comes out to Idaho in September for an elk hunt.
If you do decide to go the tarp route, be sure to learn different ways to pitch it and be careful in your site selection and it should work out great for you.
Steve