I'd have to agree alot of written sex scenes are boring, but not all, i do hate seeing lines like "for s/he was worth", its so unimaginative and formulaic. I see the same crap in news and politics when some idiot says "the fact of the matter is" which translates to "i have no idea what im talking about", its not to say that saying was always that way, but seeing it used to death and often by complete idiots makes it so for now.

and i suppose, doing any of the same thing all the time can get boring, like always being domme or sub. Of course that could be a little dependent on teh parties involved.