I had a chance to see The Grateful Dead shortly after moving to the bay area. I didn't and it turned out it was my last and only chance. I also had a chance to see Johnny Cash in 2000 and didn't. I'm no longer making these mistakes.
In the last two years I've seen Leonard Cohen, Dick Dale, Glen Campbell, They Might Be Giants, B-52s, Richard Thompson, Jeff Mangum, Skattelites, The English Beat, Mountain Goats, and about 25 more acts. Before the end of the year I will also see Wilie Nelson, Styx/Gowan, Crosby Stills & Nash. Seeing live music has nearly completely replaced going to the movies for us and it's been freaking fantastic. I've seen at least one live music show every month since March 2010.
Don't wait one second to see the acts you love live! The only downside is the $125 tickets and ticketing fees which explains why U2, Red Hot Chili Peppers, Neil Diamond and the Who (is it really "The Who" anymore?) aren't on my list yet....