I've done it twice, once in August 2005 and once in April 2004 and loved it both times. It's very similar to swimming with the dolphins. There's an introduction periods and then you get in the pool with about 8-9 other people. You get to pet, kiss, and hold the sea lion while in the water. There are some tricks such as holding hands with another person to create an arch and the sea lion jumps over you, etc. At the end you get out of the water and have a hug and kiss goodbye. The whole program runs about 30-40 min. I found I enjoyed this just as much as the dolphin swim (and it was cheaper). I didn't plan to do it in August 2005, but our snorkeling trip was cancelled due to rough water (thanks Katrina!) so I had to do something else with the kids. They all wanted to swim with the sea lions again.
We did the sea lion swim in May. It was the highlight of our trip besides the swim with the sting rays. Our friends swam with the dolphins and I'm glad we chose the sea lions. They were grouped with 12 other people so they didn't get much time with the dolphins. There were only 2 other people in our group so they let us play with the sea lions a little more. Don't forget to check out the pictures that they take of you!
my daughter did the sea lion and the dolphin encounter at chankaubab. She was 16 at the time, and I think the sea lion excursion was more for the younger crowd. It was the usual -- pet the sea lion, kiss the sea lion, etc. But, if you have never done the excursion, it should be fun.