Tonight was my Masters Swimming workout. The "masters" in the title refers to age (18 and up) and not ability level. Our group has two workouts, one for the beginners, and one for intermediates, and I am swimming with the beginners. We generally have four or five swimmers in each lane, so we get a little friendly interaction with the people in our lanes as well as a workout.
In my last masters group, there was actually one person who was just learning to swim, but I think it would be hard to learn that way, because there is usually one coach for 30 or so swimmers. Private or semi-private lessons would probably be better in that situation. If you have some basic swimming ability, though, masters swimming is a great way to improve your skills and get yourself in the pool at least once a week. You can search for a group near you on the U.S. Masters Swim webpage. My group charges a fee to pay for coaching and facility use in addition to the USMS dues.
When I swim on my own, I tend to just do a bunch of laps. In tonight's workout, however, there were one-armed swimming drills, "Tarzan" drills (freestyle swimming with the head out of the water, really stretching arms out in front with each stroke, as if grabbing for vines), and kickboard sets with all of the different kicks. I am terrible at the dolphin kick, the kick used for the butterfly stroke, but even a bad dolphin kick works the abs like nobody's business. I know I will wake up feeling that one tomorrow morning! The coach was able to give me some feedback on how to improve that kick, and that's one of the benefits of the group -- the chance to get some expert feedback and advice.
I have heard that swimming is not the greatest exercise for weight loss, but I think it's a great all-over strength workout, as well as a great workout for your core muscles if you do it right. The water provides a lot of resistance and you have to hold in your abs to be able to move efficiently in the water as you rotate for the strokes. I think that as long as you don't go on the Michael Phelps diet (at least unless you are working out 6+ hours a day and have the metabolism of a guy in his 20s), it can be a great addition to your fitness program.