i'm always looking for ways to earn a little extra cash. i used to do focus groups. they generally pay decently -- somewhere around 50 to 100 bucks for an hour or so worth of work. it's not regular work, though, and they usually don't give you much notice. so, when i started getting busy at my regular job, i found it difficult to pick up any of these gigs. i probably haven't done one in over 5 years.
i do try to pick up side projects whenever i can -- very rarely do i ever pass on an opportunity when someone asks me if i have some spare time to do some work on the side. again, it's not regular work, but it'll usually mean a couple extra bucks every now and again. and since i can sort of plan around it, it's much easier to fit into my schedule.
there's no way i could pick up a part-time job to earn more -- i just don't have enough time in the day, but i know several people who do that. there are a lot of part-time opportunities out there for people to supplement their income.
to me, any little bit counts. and a big part of it is maintaining good contacts and keeping your eyes open for opportunities out there.