SATs are more or less glorified IQ tests. So if you trust the IQ system, there you go.
I think one of the key areas of intelligence that IQ measuring misses is rationality, and therefore SATs miss that -- the ability to think critically about things at a higher level, not just solve an immediate problem as instructed, which ought to be at least equally important for someone entering university or such. IQ testing has some pretty obvious limitations, and yet it tends to get treated as litmus test with a finality it doesn't really deserve.
There's a good summary of a key book about the issue of dismissed rationality
here on a rationality blog I've brought up before, Less Wrong. The book is called "What Intelligence Tests Miss" by Keith E. Stanovich, and it's not hard to get ahold of. It explains why George W. Bush's detractors were so startled to discover that he scored well on IQ tests, in spite of some of the ways he acted which seem "unintelligent" or "lacking common sense"; Stanovich proposes that George W simply lacks the kind of critical thinking skills and intellectual curiosity which don't show up on IQ tests (or, by extension, tests like the SAT).
I can't tell you what a good or bad SAT score is, though.
Two general principles I keep in mind are 1) that tests like the SAT are fairly incomplete as evaluations of your intelligence and reasoning, so you shouldn't feel too dumb if your score is lower than you'd like, or
too certain of yourself based merely on a very high score, and 2) universities in my experience don't have
terribly high standards, depending on the college/university you're aiming for, where you are/the school is, and what kind of course you're trying to get into. (Humanities, for example, should be easy.)