I ride in the bike lane most of the time, in the left half of it to be out of range of car doors. Depending on traffic, I often take the lane before intersections to avoid right-hook collisions. (My state's driver's handbook is pretty clear on drivers being required to merge into the rightmost (bike) lane before turning right but hardly anyone actually does this.) I also take the lane when making a left turn, and when there isn't actually room for someone to pass me safely on the left but there might be room for a poor driver to think he can do so.

I don't use bike paths much because (a) separate bike infrastructure doesn't go most places I want to go and (b) when it does go where I want to go, separate bike infrastructure is often infested with headphone-wearing joggers who can't hear my bell so I have to go very slowly or weave between them. When the joggers aren't too numerous (e.g. if it's raining) I do enjoy bike paths for recreation though.

I started biking for transportation when a friend gave me a bike that had been sitting in her basement for a year gathering dust. It turned out to be as fast as taking the bus and also a lot cheaper. I had a low income at the time, so frugality was a huge motivation, but it turned out to be fun as well. There's also a great feeling of freedom in not having to check the bus schedule before you go somewhere. (For various reasons car ownership is not a viable option for me, though I'm thinking of getting a zipcar membership.)

My first transportation bike was a 40lb mountain bike, but when I moved to a hilly city this year the weight was a problem. I didn't shop around much for a replacement, just got the first road-bike-like-thing I found at a garage sale. It has upright handlebars but otherwise appears to be a standard road bike (except for being 40 years old and French and having nonstandard bolt sizes, but what do you expect from a yard sale?) and I'm very happy with it. I can go straight up hills where I used to have to get off and walk.

I suppose I am getting health benefits from biking, or at least it seems to be getting easier with time, but exercise isn't really a goal for me. I rarely bike fast enough to get tired or out of breath.