I race and train on the road. I mountain bike for fun and I commute whenever I can.
My commute: My ride to work is about 4 miles. It actually takes me about 4 minutes less time to bike it than it does to drive it. My town is about 22,000 people so its not metropolis by any means but it has its challenges. The only bike lane in town is nothing more than a no parking zone with a white stripe on the road that extends for about 4 or 5 blocks in a very low bicycle travel area. It is there because it is part of the Katy Trail that bypasses some active railroad tracks to reconnect with the regular trail just on the edge of town. The most direct route to work has a shoulder along the 4 lane road with a turn lane but the drain grates would swallow most mountain bike tires so its not ridable. Traffic is too busy and the speed limit is 40 mph. The general public is not particularly bike friendly they just don't really want to kill anyone. So they usually give you room but it is not because they know the law or even care too. I cut across a parking lot or two and use the Katy Trail bridge to cross Hwy 50 so I don't have to wait at the light 2 blocks up. Its pretty good really. I don't get too much trouble and I've even met a few people I otherwise wouldn't have. All in all not too bad.
Training: My training rides usually consist of 2+ hour 30mile and up rides on the various letter highways around the area. My town used to be and still is somewhat of a hub for farming and the railroad so there are unlimited loops you can ride. I usually leave town on one 2 lane highway and connect to another going perpendicular and then catch another highway back to town. You can make these loops as short as 15 miles or as long as you could ever ride in a day. Most of these highways have no shoulder. There are absolutely no bicycle signs of any kind. I've had a few close calls with younger drivers mostly trying to go by me the same time they are meeting a car coming the other way. I've gotten a few honks from time to time. Some times drivers even hong just to let me know they are there. My friend Matt has had one instance of a guy swerving all over the road that threw a beer at him out the window while running him off the road but it was an isolated insolent. The roads are in fair to good condition I wouldn't rate any of them as poor. except for a select few spots.
Mountain biking: Good old Mid-West single track. Radiant Trail at the Bothwell State Park Sedalia. Cave Hollow in Warransburg MO. Opossum Hollow Knob Noster State Park. Chubb Trail St. Louis. just to name a few.