A potential flip-flop

Before even beginning to train (or even sign up) for it, I'm already having second thoughts about a marathon in May/09. On the one hand, I think training for and running it would improve my overall running fitness in a huge way. This would obviously carry over into the triathlons I'll be doing next year as well. But on the other hand, I'm worried that my biking and swimming would suffer as a result. It's not as though I kick ass in either one - I can't just rely my on base fitness to pull me through. If I was to focus on running 3 or 4 times a week and use the other days for swimming or biking as cross training (instead of detailed training workouts), I don't think I would really be improving my abilities in those areas. Plus I just added weight training to my schedule - I don't want to back off on it because my running mileage (and thus recovery time) is increasing from week to week. Now I'm thinking that a half marathon would be the better way to go. I would still have to focus a little extra on running, but obviously not in the same way as a full marathon. It's a distance I know I can do and recover from relatively quickly... this past spring I did a half marathon on a Sunday and then a duathlon a week later, with no pain or troubles to speak of. There is another reason (and maybe the REAL reason) I think I might be better off keeping it at the half marathon distance... in the past, with some races I've bitten off a little more than I could chew. Case in point: Muskoka 70.3. Going in, I hardly thought it would be a walk in the park, but I never dreamed for one second that it would be as tough as it was. And now, somehow I have let it creep into my head that it wouldn't be all that tough to run a full marathon... you know, just slowly increase mileage every week, blah, blah, blah... piece of cake, right? Ya, right. Hearing some marathon stories from athletes with much more experience (ie - in way better shape) than me has led me to believe that there is a good chance that I would probably take the preparation too lightly... even though it wouldn't be on purpose (if that makes any sense). I'd do all the workouts, but maybe not with as much intensity as I should... or something like that, I'm not really sure. Something caused me to bomb the 70.3, maybe it was that. I guess the short version of all that is... a marathon scares the hell out of me right now. I think I might be better off if I was to focus on improving what I already have, as far as base-fitness goes. I'd really like to increase my strength & power on the bike, and I don't know how much I could do that if I was focused on running a marathon. Or maybe I'm just making excuses because of the bad 70.3 experience... I don't know. And maybe I'm wrong, but I think the improvements I could gain on both the bike and run by not doing the marathon would outweigh what I could gain in running only if I was to do the marathon. I haven't fully decided yet, but as usual, time will tell.