Okay... I hate to be the one guilty of bringing this up again. However, having found DD to be a very surprising treat, this thread is the reason why I picked up a copy of Pi.
DD is an off-beat hollywood flick while Pi is a super low-budget arthouse flick. The basic premise of DD is patently ridiculous so after you make the initial leap suspending disbelief is relatively easy. The plot twists, inconsistancies, etc. are a blast to try to explain away. DD is a fun movie to try to unravel.
Pi, on the other hand, begins with a much more down to earth premise and takes you on a wild ride of insanity. Unfortunately, they made a film about a mathmatician without bothering to consult one. (or a Computer scientist for that matter) It makes some pretty lame hacker-movie mistakes (although nothing so grandiose as a flick like Hackers) and is full of a lot of really stupid little mistakes that tend to be quite jarring.
Warning: Spoiler! (Click to show)A couple examples off the top of my head from the first viewing:
-Max's computer runs intensive stock market analyses which are supposed to eventually expose the nature of god in about a tenth of a second. Hot damn! Sign me up for one of those machines!
-After he fries his processor he says he lost all his data. The stock broker people tempt him with a top-secret superchip which he naturally snaps up. This chip is pretty amazing. It must operate on some wierd multi-voltage system totally unlike binary because it only has 4 pins on it. It plugs right into Max's computer board though and fires right up, ready to run Max's program on a floppy full of Koran text. Bam! So... The data he said he lost when he toasted his CPU was either stored somewhere else, totally unbeknowst to Max, in the room-sized computer he appears to have built himself, or the new CPU came with it pre-loaded. Let's just say the miracle 4-pin superprocessor that can adapt on the fly to run with hardware and software designed for a completely different processor is psychic too and call it a day.
-Max (a mathmetician) says to a Rabbi at one point "I'm sure you've written down every 216 digit number" and goes on to make a plot critical point based on that. *If* you could write down a trillian numbers a trillion times per second (well beyond a modern super-computer) it would only take you about 3 x 10^175 times the age of the universe to write out every 216 digit number. A guy whose life is Math probably wouldn't base an argument on such a statement.
-The kabalists believed that the name of god was 216 letters long, and thought that the 216 digit Max had discovered was the numeric representation of that name. Max's number was base 10 though, so it would have been limited to the first 10 letters of the hebrew alphabet and would not have matched the hebrew number system which represents numbers with letters. (It doesn't just number the letters from 1 to N. Some letters have values in the hundreds.) If it were to be capable of representing all hebrew letters it would have had to have been 432 digits long. (This assumes there are 11-100 Hebrew characters. You could actually represent a 216 digit hebrew number with fewer than 432 digits if you used a smarter encoding method, but somehow I think it would have been beyond the ancient Hebrews.) Perhaps a better question is whether a 216 digit Hebrew number would even come close to a 216 digit base 10 positional number. Hebrew numbers weren't positional. The largest number represented by a single Hebrew character was something like 400 (correct me if I'm wrong) so the largest number a 216 digit hebrew figure could represent would be 86400. This is academic though, since there would still be (1 * 10^216)-1 different ways to write the number assuming that hebrew numbers didn't have any order-specific syntax like midevil scholars imposed on the roman numeral system. (e.g. IV would have meant 6 to a roman, not 4.)
-The rest of the math is pretty pathetic. You would think that an equation for the universe would be a tiny bit more esoteric than pythagoras' golden spiral. (Although it does admittedly make for some neat visuals) This movie is a great example of what happens when an english major decides to write about something they know next to nothing about.
The form and visual style of Pi is utterly captivating though. The acting is top notch. Just don't pay too much attention to the plot or details and it's a wild ride. I enjoyed Pi immensely, but I think DD was a lot more fun to try to figure out after the fact. Someone said previously that Pi put form before substance. I couldn't have said it better myself. But what form!
) I got the majority of it. I haven't seen a movie that's haunted me like this in a long time. I plan on purchasing the DVD this week so that I can watch it with my wife and get her input as well. I also plan on introducing this film to my family over the holidays, I'm sure that it will generate some interesting discussion. Can't wait! 
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