| Well, it may not be allowed in SAT and whatnot, but it definitely was forbidden in every single mathematics exam I had in lukio (Finnish equivalent of high school, roughly), including our graduation exam (matriculation examination). No wonder, either; like said above, it can solve equations, integrate and differentiate, even if it's pretty limited. Not exactly knowing what the machine does, I'd guess it has some builtin shortcuts to most common integration problems and basic formula fiddling mechanisms. Even if it understands basic logic (you can use 'and' and 'or' in the symbolic solver), it breaks down quite fast with anything non-obvious, such as most of modular mathematics I asked it.
Also, its programming language sucks. No, seriously. TI-BASIC is evil. However, TI-GCC supports 89, which means you can actually move to writing real games, and with 256k RAM and 512k archive of slow-write memory (a sort of modifiable read-only storage) it's a bliss. If only the archive didn't occasionally get totally screwed up for no reason at all. | 
