There is an entire sub-plot cut from the original release involving Healey's friend, Sulley, where he is a Policeman and recovering drug addict/alcoholic. He has been clean for 19 months, however, after being re-aquainted with Healey he returns to drugs and is eventually eaten by his own pet python. This sub-plot is reinserted into the Extended Cut.
When Ted is helping the old man in the wheelchair carry furniture into his house, the old man drives away in the wheelchair. While driving away, he gets caught on a little tricycle and pulls it along with him. When it shows Ted from the front view going up the steps, the tricycle is sitting where it started.
What are the differences between the theatrical version and the Extended version of the movie?
The "There's Something More About Mary"-version features a longer cut of the movie that is way more raunchier and naughtier and contains scenes that presumably had to be cut for the theatrical release of the movie. This new version runs more than 10 minutes longer and is worth a look. A detailed comparison between both versions with pictures can be found here.