I do both, depending on the gig. I do tend to stand for more high energy gigs, and sometimes sit for restaurants and lower energy jobs. I know my playing and pedal work is more precise when I sit, but it just feels wrong when the energy starts rising (and I can't afford one of those motorized keyboard stands, or take the weight! Donny will probably post the URL for it LOL
).
However, as I get older, I find after a long summer of playing standing every day for hours, and the twisting that puts on my knees (one foot is always on the sustain, so you can't always balance yourself well when you have a big 76-er to cover!), I am starting to get some pain just walking any sizable distance until I get a month or two off (I mostly just do studio work in the off season), so it may not be long before I will have to sit for ALL my gigs... But I will hate it!
If the music doesn't make YOU dance, how can you expect it to move your crowd?!