I live in MI, and for the past few years I've been setting off towards the plains whenever an active period is forecasted (i.e. 6/3/05-6/12/05, 3/29/06-4/2/06) and my "standards" are just a tad higher given that I typically have to spend the most money and drive the most miles in order to chase the "traditional" setup. Consequently, I guess my idea of classic bust days would days like 10/22/04, 5/7/05, 6/4/05, and most days in May 2006. Yes, I'd have to say most... I typically have to drive a thousand miles in order to even reach the dryline, ergo, I often like to see convection in a form I couldn't see it in my home state -- e.g. classic, photogenic supercells, which 2006 didn't bring in May or June. Instead, it brung it on several days in the late summer, when I was left flat broke.
To break it down, a bust to me is both the classic "cap" bust and elevated or non-photogenic high-based crap. When chasing, I expect and pine for storms with sustained surface-based inflow.