Just got mine today - let's see how I feel tomorrow.
The vaccination center I went to was well organized, as expected, but in the 25 minutes total I was there, I think I saw 5 other people getting vaccinated compared to the 30+ total staff. Either people don't feel much urgency in getting a booster, or Monday afternoon isn't a popular time for it, or maybe both.
I went to the vaccination centre in Minato sports park on Friday. The Pfizer side seemed to have some waiting time just to get in, the Moderna side was basically just walk in. Though there was a steady stream of people, they were nowhere near running at full capacity.