If you apply the same weight consideration of tent vs. tarp (choosing the twice-as-heavy option) to the rest of the stuff in your BOB, the BOB will weigh a whole lot and will be an impediment to your bugging out, much like a boat anchor.

If weight is so slight a concern, then it is not really a man-portable BOB, it is a car camping rig.

People who don't believe that "ounces become pounds, and pounds become pain" have not put in the time under a heavy ruck.

Quite true. And that's mostly what I'm looking for. I have no illusion that I'm going to be walking off miles and miles into the wilderness to survive for years with nothing more than the BOB on my back. That might be a fun fantasy to think about, but it's not realistic. Pretty much the BOB would be to get from the house to the truck, drive a bit, then from the truck to a nearby camping spot, then back to the truck, etc. It wouldn't be for a cross-country march. If I have a 72 hour bag, well, that would just about get me the 30 miles from the north end of town to the south end (if hiking). And I'm not sure why I'd want to hike down to the south end of town in the first place.

I'm not in an area that has large scale disasters. No flooding, no hurricanes, no earthquakes, no volcanoes. The occassional small F1 tornado that might wipe out a block or two. But that's about it. I guess we could get nuked, but walking miles and miles through the radioactive fallout doesn't sound like a good idea.

So yeah, pretty much a car camping rig is what I think would be most useful. But I would want something that I could get from the house to a car, or from one car to another. So I don't want an ungainly 10 cubic foot 200lb kit (but that would be nice for a "BOB" that is permanently stored in the truck). Hence the backpack container for it all. "Portable enough" for short transfers, but not really a hiking rig.

If you are planning on using it with your truck it makes the choice much easier. Get a tarp, use the shell on your truck for normal shelter.
When you can't do that you then fall back on the tarp shelter.

Well put. In that case, I would go with a deluxe 3-man tent which means it's decently sized for 2, yet still packable. The REI-branded tents are a really good value. I recently compared the REI, Big Agnes, Nemo, and Marmot 3-man tents at the local REI store. I set up, inspected, and broke down each one.

I went with the Marmot LimeLight 3. I feel it is well designed and constructed. It includes a custom footprint which can be set up with the fly and poles alone if desired. Major material selections (floor, zippers, fly, etc) were about 1 notch heavier duty than the other brands. This made it ideal for car camping. This is not a dig on the other tents, they have to make those compromises to shave 1 or 2 pounds, which is a big deal when on foot.

I agree with looking at the purpose of the BO (Bug Out). All-in-all the tarp is the option for me. The tarp, as has been pointed out, is far more versatile.

It wouldn't be a good idea, I have to agree.

I'm expecting we'll get EMP'd rather than explosively nuked and have built my BOB strategy on that basis. The EMP scenario puts one afoot a long way from home where the supplies are. The environment is benign but without modern transport- it's a long way home. Hopefully there won't be massive riots in downtown Niwot.....

I hope not! Niwot might be one of the places I'd be bugging out to! I'm right around the corner, so to speak, in Broomfield. I don't think I could make it much farther than Niwot if I were hiking...

A 6th option is the tipi:
http://kifaru.net/tipis.html

Though you could probably do this with a big enough tarp.

A seventh option would be a nice rock shelter - no weight at all, and extremely protective. They are very common on the Colorado Plateau, especially in Four Corners country. Too bad if you are elsewhere......

My best nights outdoors have been in such shelters.

Have you been putting those rocks in other people's packs again???