I quit smoking and started running and lifting weights in July 2009 in preparation for joining the military. I didn't get in, but I've still been running and lifting like a madman since then, and it's the best thing I ever did for myself.
I'm ripped as hell, feel great about myself, people respect me more (I don't bully people or anything, I mind my own business; it's just that people probably think twice before trying to screw with me) People tell me that a lot of women at my work refer to me as "that guy over there with the nice ass" if they don't know my name. Also a lot of times when I go jogging and it's hot out, I take my shirt off, then girls drive by in cars and yell "YEA BABY!!!!"

I used to really be depressed and down on myself all the time, but exercise (along with a more positive mental attitude) has put my self-esteem through the roof.
For a lot of people just starting out, exercise is a chore; something to get out of the way. But that's just how it is at first. If you can force yourself to stick with it long enough to see results, you'll be hopelessly addicted! It's no longer something I have to force myself to do; now it's something that I look forward to with excitement every day. It's usually my favorite part of the day. If something comes up and I can't go for my run or do my weight lifting session, I get pissed. I HATE missing workouts/runs. And exercise is such a good microcosm for how life is:
you tough it out and push through all the hard times, and you come out stronger than before. And in time, you learn to love a good challenge instead of dreading it.
Not to mention that exercise/fitness is a great niche and if you can write from real-life experience, you can do well. There are a lot of fitness blogs that are just some guy talking about what workout he did that day, a new protein powder he found, a guide on how to do a certain lift, etc. and they are hugely popular. In most cases, it doesn't look like they do very much SEO; they just write what comes to mind and rely on mostly word-of-mouth referrals. Maybe put some PPC ads on the side and throw in an occasional blog post about an affiliate product, and you could be making some great money by just writing about something you love.
Anyone want to have a friendly fitness stats competition just for kicks?
I weight 210 pounds, and this is what I lift:
Bench: 210
Squat: 255
Deadlift: 300
Overhead Press: 210
Bent-over Row: 265
Barbell Curl: 115
Can do 80 pushups, 8 pullups, or 5 pullups with a 25-pound kettlebell strapped onto my waist
Run 3.5 miles 3x per week; longest I ever ran nonstop was 8.5 miles