It depends on my mood. Right now, I have a bit of downtime before I start the next phase of my life, and as I have a lot of items left unreviewed (I ordered 10 items earlier in May), I'm writing about one a day.
I usually write one a month at this point in time. I get one done in time to pick out a new item to review. I don't have very many extra items yet other than the one I get to review every month. I might write them more frequently in the future, though.