I'm one of the dweebs that actually knows the formula, and I can confirm that it's a stupid one. It's actually a decent example formula to test out your programming skills on since it's so complex so you can test a lot of different things but that's beside the point.
Say Jamarcus Russell goes 1-10 for 7 yards, 1 TD (off the facemask of Darrius Heyward-Bey and into the hands of Zach Miller), and 0 interceptions (overthrew the defenders too). We can probably agree that that's a pretty bad stat line.
That's a 72.9 rating. Not great, but probably not indicative of how bad the performance is.
Four categories: Completion percentage, average yards per pass, touchdown percentage, and interception percentage. The last two categories he would have received PERFECT scores for. You can accumulate a quarter of the points it takes to reach that max value of 158.3 by simply not throwing an interception. Also if you've thrown interceptions and your completion percentage is already crap and you don't have any touchdowns, you might even be able to increase your quarterback rating by throwing a shit-ton more passes, complete or incomplete, because it lowers your interception percentage.