30 days hath September, April, June, and November. All the rest have 31, excepting February which is just plain fucked :^D
I always said it as '30 days past September...', but your version makes a whole lot more sense. Of course I learned it back when I was 6 or something, so I never thought about it much.
To remember the difference between concave and convex, the concave one goes inward, like a cave (con-cave)
Stalagmites have an M, like mountain. And much like a mountain, they point up. Stalactites are the other ones.
What is odd though is that I never learned and cutesy tricks for remembering how to tie a tie or to tie my shoes, and I never learned the state capitals in school. It was something that was done in 6th grade in my area, and I went to a private middle school where they didn't teach that for some reason.