Personally I don't see a situation that long term as being all that likely even in the worst of circumstances (barring a global pandemic or a nuclear winter that wiped out 95% of humanity).
Even in the case of an EMP strike that took down the entire North American grid the mayhem would likely only last a couple of years, and then some form of structure would be imposed. Times may still be very hard, but it wouldn't be "Road Warrior" levels of chaos as foreign powers would move in to start colonizing parts of the country.
As far as survival groups, I suppose those groups that have actually acquired a shared B.O.L. would have a practical purpose, but honestly I get the feeling many "internet" groups are more about fantasy roleplay than practical survival plans, and I seriously doubt if many of them could get along well if the s really did hit the fan. While I do not follow an organized religion I do think the Biblically based groups will have a better success rate especially with regard to infighting, which will likely be a BIG problem for most other groups because they never laid out clear goals and hard limits from the start.
Personally if the shtf I would plan to go it alone (well me and my dogs, so mobility would be out of the question for us). We wouldn't survive long term, but I hope to be prepared to make the best of whatever time we had, and "buying some time" to figure out how bad things are while maintaining some control over our fate would be the ultimate purpose. Even just being able to hold out for 2-3 months would allow one to determine if it was truly a long term SHTF situation or whether it was a temporary glitch that could be resolved (of course if I had dependent children that that would complicate matters considerably).