I seem to go several weeks without new points, and then get two or three batches in rapid succession.
When I first started getting them months and months ago it seemed like I was getting them constantly, with just a few days between the expiration of one batch and receiving a new one.
Then I started getting requests to metamoderate, and the regular mod points started coming less frequently. At one point Slashdot would ask me to metamoderate three times a day. In recent weeks that seems to have dropped to twice every 24 hours, or maybe I'm just not checking as frequently.
I'll try to start recording how often I'm offered moderator points, just to see if there's any rhyme or reason to it. I rarely use my full complement anymore when I do get them, because I can't find any meaningful posts to moderate when I have points available. (I try not to use them to slap people down as much as to encourage worthy posts, and I metamoderate the same way.)
And of course, once the latest batch of mod points expires I always find a thread with lots of worthwhile posts...