after many years without a bike, i bought a mountain bike about 3 years ago and was immediately hooked. i've gotten into cycling for fitness just as much as fun, so i made the jump to a nice road bike toward the end of last summer and really enjoy that now. in addition to being great exercise, i really like that fact that i can head out on my bike and just be alone with my thoughts as i pedal along...great stress reliever after a long day at work. i'm not a hardcore cyclist by any means, but i'm slowly working my way up on the road bike this year. it's definitely the most enjoyable form of exercise i've found.
as for pointers, my two biggest suggestions are to make sure you have a bike that fits you well, and don't be afraid to buy some padded cycling shorts. having the proper fit for your bike will make your riding much more efficient, and you'll be a lot more comfortable in the process. many of the aches and pains you get from riding can be remedied by having your bike properly fitted. the cycling shorts are important because that little bit of extra padding in the rear is crucial if you're in the saddle for very long, and the slick fabric prevents chafing as your legs rub together. if you don't like the spandex, look into some 'baggy shorts'...they look like regular nylon shorts but have the padded lining. i often wear them when i know i'm going to stop somewhere not because of the look, but because mine have pockets that make it much easier to carry around keys, money, or anything else i might need.
one other suggestion if you stick with cycling for a while...strongly consider trying out clipless pedals. most people are initially afraid of the idea of their feet being attached to the bike, but it makes a huge difference in your pedaing efficiency. your form will be better, and you'll be able to exert force on the pedals throughout your stroke, both as you push down and while pulling your feet back up. when you first start out, you'll feel the difference as you're using new muscles, but it pays off in the end. when i ride without being clipped in now, it feels odd because i'm used to pulling the pedals up with my feet on the back side of my stroke...both legs work all the time, giving you more power throughout your pedal stroke. it's definitely something to think about if you want to get into more serious riding.
as for my bikes, i'll snap some pictures in the next day or two when i can do them outside in the sun...lighting in my apartment right now stinks. i'll get them up soon though