Like Beth, I'm a relatively average runner. She is faster than I am, but I suspect with work I'll top out right around where she is. I'm solidly in the middle-of-the-pack, and as near as I can tell, people don't develop speed when they start running in their thirties. I'm out there, and I enjoy it.
But I wouldn't have been 15 years ago. I am slow. I am in the weird position of being fit, but slow; I'm just not a gifted runner naturally, and I have almost no background in it. So when I tried to take up running in my twenties, there wasn't nearly as much advice, running hurt, and the only people I knew who ran had run for their high school teams, which made it hard for me to jump in. I had to be in my mid-thirties, post-kid, post-caring, before I could face a couch-to-5K.
In the meantime, everyone started running, including those slower than I, so now I'm in the middle of the pack.
And now it seems like everyone and their mother is running a marathon. Halfs are even more popular, for good reason. Marathons are a dumb distance that kills young Greek men. Halfs are just long enough to disguise the fact that one has no leg speed.
Seriously, though, I can see why it would annoy someone who was a serious amateur athlete to find that their sport is now cluttered up by people chugging GUs for a 5K that they're running in tutus and perfectly coordinated expensive gear.
Still, look, people need to get over it. Running is a better sport when it has more participants. Many people are finding a hobby they love and a way to stay in shape, and that's hard to knock. Plus, more participants means more races; sorry if your finisher's medal for being sub-sub-elite is the same as the hobby joggers, but newsflash: unless you're in the first three, you were racing the clock anyway. Even if you were totally all-county in high school.
That said, I won't be running a marathon any time soon, because for me, I don't want to just finish it. I'm in excellent shape. Of course I can walk 26.2 miles if I have to. That's not a challenge, just a hell of a long walk. If I run one, I want to be able to race it at least a little, and I do not have the experience yet to do so without injury, and I'm slow enough that the time commitment for training is rather daunting. I also wonder if there's too much push to do marathons. I think some runners of my acquaintance who are running to get in shape would be injured less if they focused on running short distances first.
But halfs are nice. So far I think they play to my strengths as someone without any speed but with enough willpower to complete a training program.