Perhaps I'm missing something, but it seems that the rules for the daily reputation cap are changed on a pretty regular basis, and it's got to a point where it's quite hard to get an idea of what its current state is.
I intuitively go to the FAQ for such info, but over there it's only referred to in passing, not once explained. Is it perhaps because the rules change so often that they're not in the FAQ - because it would too swiftly become outdated anyway? It appears that currently you have to stumble upon it to know that it exists at all.
Since there can be reputation changes that does not affect rep cap - such as accepted answers - it could even become a bit tricky to know when you've reached it. Ideally, I would like to see in the recent tab, "You have another 30 reputation to gain before your daily reputation cap for this date is reached" - where the emphasized text would be a link to a FAQ entry explaining the feature.