I'm sure this has been discussed before, but I couldn't be bothered linking to the previous thread.
I stand - with the 'board at an increased height (similar to if I was seated at a Piano).
Just my opinion/thing/problem, but I feel I'm "not giving my all" or even "ripping off" the audience if I don't stand and, yes even groove. (It's an audience interaction thing for me as well).
Oh yes, and as we're primarily a "vocal act" so I personally VERY much need to stand for breathing/singing purposes.