Fun with cardio & numbers
I'm not sure if it is having a year of practice under my belt, or having lost about 20 pounds, or some combination thereof, but I'm noticing with my runs this year that I can go much farther, much faster without exerting myself nearly as much.  And of course, being the big math nerd that I am, tracking all of this stuff via my shiny toys makes it easy to compare performance over time.

Here is a chart showing my heart rate during a run around Green Lake on July 29, 2007.  Notice how my heart rate spikes up to 90% of its max (about 180 for me) right away and just stays there.  I was quite proud of this run at the time because it was the first time I'd approached a 10:00 mile for an entire loop without stopping to rest or walk, but in retrospect, I can see that I was overworking myself for no good reason:  [edit: graphs removed in favor of a link to MotionBased]

Now take a look at this one.  This is from another lap around Green Lake, but it was last night, where I struggled to not speed up past 10:00 during the first two miles, and then kicked out the last mile or so at an 8:00 pace: [ibid]

So I'm able to run faster with less effort for a longer period of time.  Personally, I can't help but think that the extra 20 pounds I was lugging around last year put extra strain on my heart.  It almost makes me wonder what would be possible if I lost another 20 pounds, which of course is something I should do.