Nope, this is not going to be a rant. I don't do those :)
When I was growing up, I spent a lot of time with my father riding bicycles. I think I was about ten when I got my first road bike and starting doing what was for me long rides through the countryside. Through high school, I rode many many thousands of km with him each year.
After attending university and graduating a couple of times, I got seriously into off road riding and spent hours each week riding in the dirt and on the road. I had a job which allowed me to set the hours, and required evening work, so I built a schedule around mountain biking. I managed to get in 24 to 25 hours a week of saddle time. My bike was referred to by my wife as "the other woman." A serious, painful, over the handlebars crash onto ashphalt caused by a dog, low psi tires, water, and road paint put my love of cycling into a tailspin and for a time I took up running.
These days, I spend a fair bit of time riding the rail trails and doing some running. I am not as comfortable doing a lot of high speed off road riding as I used to - I don't heal quite as fast as and crashes are a fact of life when you off road as much as I would like.
My bike of choice is not a moutain bike, but rather a cyclo cross bike. I use a Kona Jake-the-Snake.
I am very fortunate in that I have two very good friends who also happen to love road and rail trail riding. For us, the advantages of intercity rail trails are plain and obvious. It is possible to get a serious turn of speed on them as there are no real intersections (or rather, few of them) and often, there are no other trail users other than long distance hikers, and the occasional bike. It is not like riding on a converted trail in the city which is so full of people that getting a good spin going is inconsiderate at best, and dangerous at worst. The rail trails are also appealing because largely, we are tired of sharing the road with motorists, many of whom are inconsiderate or dangerous in their interactions with cyclists (how cyclists make things worse for themselves is a topic for another day.) Using the rail trail is a fantastic way of avoiding this concern entirely.
The rail trail we frequent (one which runs from South Cambridge to Paris and beyond in Southern Ontario) is one of the most civilized places to get a workout on a bike that it has been my pleasure to experience. The people we meet there are friendly, and open to friendly greetings. Not once have we had a negative interaction between us and other trail users (except for a few cyclists we met one day who were rammy and inconsiderate of other trail users that were going slowly. I don't like that much.) Between Cambridge and Paris, there is one intersection over a distance of about 21km, so getting up to speed and staying up to speed is easy to do.
Today's run was great. The weather was cool and crisp and there was some off again on again misty rain falling. Staying warm involved triple layering the torso, and using some leg warmers along with the usual cycling shorts (these days, I tend to use linered mountain bike shorts because pockets to hold phones, keys, and money are useful!). Again, we met some wonderful people along the way - it is encouraging to see so many people out riding.
The only off putting part of the ride were three loud bangs near the trail. I just hope that the hunters were shooting away from the trail and people's homes. It sounded like they were almost on top of us...