I have done three rides over 100 miles. The first one I set out to do on a Sunday in the Spring. Only had my Roam then, and got started much later than I wanted. I finished the last 20 miles in the dark, and it was tough. Bike didn't exactly fit the best it should have, and I was hurtin' the last 10 miles or so. Finished at 104 miles.
The second one was still on the Roam, but wasn't really planned. Just got to riding on a beautiful day in the Fall, and kept on and on. The next thing I know ...101 miles had gone by.
The last one, about 6 weeks ago, was another I didn't plan. Just set out for a normal ride of 50 miles or so, and I felt good and just kept going. This time on my Roubaix, and it was much more enjoyable. I could have went longer, but the Mrs. called me home for dinner. 107 miles.
I'd like to do an organized century, but for whatever reason just haven't yet. Most of the organized rides I participate in are from 40 to 62 miles. Some days are much better than others. I have seen days where 30 or 40 was the most I had, and couldn't squeeze another mile out for nuthin. Now that I think about it... maybe that's why I haven't yet tried to ride an organized century. It very well may be one of those puny feeling days, and I wouldn't want to feel like I bombed.