The Seminar Scene with Michael Robinson is stated to be completely improvised with 3 or 4 alternate speeches. Each of them are stated to go on for about 10 minutes and will probably be released on the Director's Cut DVD.
As stated in the audio commentary on the German DVD, the movie was intended to be more satirical and ridiculous, like "Blues Brothers meets Borat." Executive Producers Steve Wik and Vince Desiderio, didn't like Uwe Boll's approach, so he rewrote it with Bryan C. Knight.
During the big final shootout, when Zack Ward shoots everyone with the machine gun, the spent casings fall to the ground in slow motion. They're obviously blanks with crimped ends, not empty casings, which would come from live ammo.
How many different versions of Postal are available?
The R-Rated theatrical version and the US unrated version are missing several scenes included in the original German cut of this movie. In total nearly 49 sequences were left out for the US releases of this movie and a detailed comparison with pictures between both versions can be found here.
But there are even more versions available. In Germany a Director's Cut of this movie has been released with nearly 10 minutes of extra footage. Again a detailed comparison between the uncensored German theatrical edition and the DC with pictures can be found here.