Grading in school has actually become kind of an AS specialist subject for me... but that has also helped me get better grades. Whereas in my early 20's I was unmotivated, didn't do a lot of assignments, and as a result got more B's and worse than A's, now I get mostly A's.
With my math skills, if I know how many points there will be total for the semester, I am capable of figuring out exactly what I am getting, the highest mathematically possible grade, and the lowest mathematically possible grade. Doing these kinds of calculations motivates me to do my assignments, since they're usually worth a significant chunk of what I can miss and get an A.
If I don't know exactly how many points there are going to be, I approximate what percentage of each category of work (homework, quizzes, tests, etc.) is out and can figure all of the above from there. I even had a math professor for two semesters who did not post grades online, on the principle that those in this high a level of math class should be able to figure it themselves. This semester I've actually created an Excel spreadsheet where I can enter my scores and it will figure what I'm getting / range of mathematical possibility.
Here's what grades generally stand for to me:
A+ = Awesome
A = A job well done
A- = Acceptable
B+ = Bit low
B = Barely excusable
B- = Bummer
C+ = Crummy
C = Crap
C- = Christ, that's awful!
D+ = Damned horrible
D = Death
D- = Doomed to McDonald's
F = Failed all of life
Yes, pluses and minuses count in the GPA at my school.