Some time ago there was a rather lively discussion on the language blog, Pain in the English, about these two idiomatic expressions. Let's take a look at a couple of examples from Google Books:
He was sat there with his arms over the back of the sofa looking really upset so I thought there was something ...
Under the Rotunda - Danny Bernardi
In an instant Dave knew that he was stood on a road and that there was a vehicle coming ...
The Company - James McCann
And here's one with both
We saw him later on chatting to another bunch of bemused holidaymakers, only they were sat down and he was stood in front of them, in his Speedos ...
Thai Tales - Justin Dunn
Read a bit more about these expressions. What do they mean and are they grammatically acceptable?