I'm with kirk on this one. Except my 'poison' is swimming. Actually, I do some meets and long distance swims too. Traditionally, the National Championship season is over in April/May, so it coincides well with racing. But these past few years i've been doing a big charity swim here in the Northeast across Long Island Sound, which is in August. Last year Ii had to do it with two broken ribs, thanks to a qualifying (!) crash where I was the meat in a 4 wide sandwich at the Glen. I will NOT be doing the swim this year with broken ribs!
But, if there's a pool around it's a phenominal way to get in shape. Great cardio, and you use more muscles than you'd think doing it. Plus, it's not bad on the joints. I still get hot in the car, but a standard regional race is no big deal. I did a 3 hour enduro alone in August....and that was fine too, but it was only 85 or so.
So, my mantra is, fitness first, fancy stuff later.