I've read every 5000 shots but I only make it apoint to change it once a year (generally in the spring). I'm sure I shoot more then 5000 shots over the course of a year but not to the point where I'll wear a string out.

When I was younger and didn't know any better I went a few years without changing a string.

1) I personally wouldn't and I'll give you a couple of reasons why. Strings aren't that expensive. Obvious safety issues. If it should snap durring the fall and the bow dosen't come apart in pieces you'll pay hell to get it into a shop (busy time of year). If you get it in a shop you'll have a new string on your bow that will need tuning and likely will be stretching for a while after it's replaced. In complete honesty I wouldn't wait to change it. Do it now and you'll be sitting pretty when the season comes.
2) I have hard evidence either way on this question but I do. Again they're not that expensive campared to the price of your bow.
3) Not personally but I use to shoot with a guy when I was younger, a friend of a friend that I've lost touch with. He was shooting a string 2 years old and had it let go while shooting 3-d in mid August. He ended up with a nasty bruise on his arm from where the string whipped him. Luckily the bow didn't "explode" but he had a heck of a time getting a new string on because it was the bust season and them he dealt with the tuning and stretch problems I mentioned previously.