I just signed up for the BAA Half Marathon in October and a 1 mile swim in August. It's been years since I've swum competitively, but I am completely thrilled. I'm in better shape than I was in high school, though I think I technically ran faster then I had much less stamina.
I will probably need to buy another bathing suit (I have ones that are OK for swimming in the lake for fun but not for anything fast), but I'll put that off for a week or so.