The Skill Point system seems very bizarre to me. You can get 500 in a single fight, then 0 for the next 3, then 100, etc. There are some minor things that I've seemed to notice, but I'm not 100% certain if my findings are at all accurate.
The 'system' seems to dislike when you grind on the same type of mob over and over again. I was in a camp where there were Funguars and Opos (The monkeys, I forget their FFXIV name), these mobs checked as Even Match for the most part. At first arriving to this camp, the skill points were flowing in nicely, eventually it slows down. Every now and then I would mix in a Roselett (sp?) that checked only Easy Prey to me. Most EP mobs don't give very good skill ups compared to higher level ones, but these were giving me 150-200 SP a kill, which is a decent number while soloing. I was getting roughly anywhere from 80-140 on the Even Match mobs I was heavily grinding on.
I had noticed something else as well but my memory is being terrible tonight, so I will edit in any other thoughts as I can remember them. Anyway, feel free to add anything you might have noticed as well. And lastly, I was curious if doing a Battle Regimen successfully sometimes gives extra skill points? I wanted to test it but my friend and I pathetically could not pull one off in the 15 minutes we tried =(