I had a recent Southwest Airlines flight that required me to change planes at the San Diego International Airport. I was reluctant about this particular flight since it was 30 minutes between when my flight arrived and my next flight departed, but I felt pretty safe, as I had flown into San Diego on Southwest twice in the past year and Southwest flights were contained in a small circle. It wouldn't be a big deal to quickly walk to the next gate as long as there were no delays, which I have not had happen with Southwest at my airport of origin.
What I didn't realize, however, was that Southwest also had gates 1 and 2, which are separate from gates 3 through 10, and require going through security. This was a difficult enough chore for me, just carrying one bag and experienced enough to get through security relatively easily and quickly. Still, I had to run to get to my flight on-time, though it is not a far distance from security to the gates. I can only imagine the difficulties older travelers, inexperienced travelers, families, and anyone further back in the plane would have.
Still, I got lucky. When I was leaving San Diego back in August 2012, the security line curved all the way back to about midway down the baggage claim area. If it was like that with my recent flight, I would not have made it in time.
If you have a Southwest flight where you will need to change planes in San Diego, make sure there is at least an hour between flights to be on the relatively safe side. If all of your flights are at gates 3 through 10, you'll be able to take it easy. If not, you should hopefully have time to spare after going through security again.