Inspired by this MSO question, I think it would be a good idea if the flag dialog shows the daily limit alongside the number of remaining flags.
Currently, the message at the bottom right of the flag dialog says:
You have xx flags left today
I propose that we change it into something like:
Flags left for today: xx of yy
or any other wording that would include the two pieces of information.
This has two benefits, in my opinion:
It allows you to know your current daily flag limit without having to calculate it (or check it at the start of the day).
It allows you to quickly check how many flags you've already spent today.
Could this info be added to the flag dialog?