While some orchestras and ensembles I play in rehearse once a week, usually when I get hired to play for an orchestra, it's two rehearsals and a concert. Add that to the other groups I play in, and it's just not worth it to memorize music. If ai did show up to an orchestra concert with my parts memorized, I think the only thing I'd do is piss of the other musicians around me. And my intonation usually takes care of that.

But sure, try memorizing the first bassoon part to the Verdi Requiem.