Well, an A+ is worth 4.3, so if you're some kind of superhuman I suppose you could get a 4.3 overall, though it's not really practical when you're taking 3 classes a quarter and being a TA or RA. I managed to get three of those, and honestly I think I earned them - I worked extremely hard throughout my MS and that occasionally resulted in very strong results. There are some classes with inflation-compatible grading schemes (Pat Hanrahan's 148 comes to mind, in which, when I took it, 7/8 projects offered 25% extra credit each, and each project was 10% of one's grade, meaning the maximum grade for the course was 117.5%...though I didn't get an A+ in that course, since I didn't do well on the exams), but they're the minority.