On "might could": I grew up in Tennessee and now live in Georgia. I grew up hearing and using that expression--and I still use it in colloquial speech, even after learning to regard it as "non-standard usage" and an example of a "double modal" in my later study of linguistics and dialectology. ;)
In my experience, though, "might could" has a shade of meaning that "might" and "could" do not have on their own. "I might do it" indicates doubt about doing the thing; "I could do it" indicates conditionality, ability, or ability in the past; "I might could do it" indicates doubt about the ability to do the thing. "I might could do it tomorrow" means something like "It's possible, but not certain, that I will be able to do it tomorrow." I've grown to have a great affection for the precision of double modals and use them quite gleefully now, but would likely modulate to something more standard in more formal situations ("I might be able to" instead of "I might could," for example). :)
And now, something I overheard at work. :) "Yeah, I was all about saving money when I was in college. When I was a senior I even went to some kind of talk that Clark Howard gave, and he was talking about how his wife shops at consignment stores, even though they have so much money now. That was the end of the whole Clark Howard thing for me--I mean, if shopping at consignment stores is the end point, then it's just not worth it to me."
(edited to clarify who gave the talk!)