one of the best things about starting something like this is that if you stick with it you get to watch the improvements as they come. you can see where you started and where you are now and have a "yay, me!" moment because of how far you've come.
and i've come a long way. starting from the "couch to 5k" program i've gone from jogging 60 seconds straight to being able to do 3.5 miles with relative ease. seriously. i did 3 yesterday at a very easy pace. today i did 3.5 at a slightly faster pace than yesterday's 3. and they were both pretty easy. never once did i feel like i was sick or terribly winded or anything. and that feels great! i feel fit and strong.
and while i'm not necessarily in the best shape of my life yet, i definitely have the most endurance/stamina that i've ever had. even when i was in weight training in high school and benching 125 regularly i couldn't run 3.5 miles straight (i don't think--i never tried though i did 3).
now, if i can just add in some appropriate (and fun) cross training and a little bit of weights on off days i'll be a force to be reckoned with!