Random Facts and Gaffs from Plan 9
009: Plan 9 From Outer Space
I did a little googling and came up with some fun links. So far, the best is a site detailing all the mistakes in the film. The man found 73 of them. I think my favorite thus far is "The flying saucers are making noise--IN OUTER SPACE!!" He also points out that it shifts from night to day incredibly often.
Also, IMDb has some decent trivia. Did you know that the film was funded by a Baptist church and the entire cast let themselves be baptized? 'Tis true.