I was wondering whether this should go in the Gig thread, but thought it'd be good to separate this purely to talk about what your biggest regret was in terms of bands you never got to see, passed up the opportunity, saw them too late etc etc.
Obvious one for me was Prince. I had the chance to see him while I was Uni. However, being a poor student, I couldn't spare the money to go so had to pass. A few years later, once I was out of Uni and back working, he announced his piano tour. Went online as soon as the tickets were due to go on sale, only to find that he'd cancelled the tour as he was unhappy with how much the promotional companies were charging the fans for tickets (very admirable, of course). He'd said that he would rearrange the tour at a later date, and then unfortunately he passed away not long after that. My absolute hero and I never got to see him live.
Had a couple of chances to see Rush when I was younger too that I passed up. Shame.