Like Chuck said, trying to use the saw fence for the router just isn't worth the hassle. There are just too many times I go back and forth between saw and router. Then there's dust collection to think about. Lots of the better router fences have a way to hook up a shop vac hose to the fence and catch a lot of shavings. Those shavings would have no where to go and would build up if you just cut a mouse hole in an auxiliary fence and attach it to the off side of your tablesaw fence. I have my router table in the extension wing of my saw for space considerations, but I also raised my saw 3 1/2 inches on a 2 x 4 base. That's mostly to provide clearance for boards that hang over the left side of the saw to pass over my joiner fence. However, like Bob said, I wouldn't want the router table to be as low as a standard tablesaw. If I wasn't already cramped for space, I'd have a dedicated router table.
“We should be careful to get out of an experience only the wisdom that is in it and stop there lest we be like the cat that sits down on a hot stove lid. She will never sit down on a hot stove lid again and that is well but also she will never sit down on a cold one anymore.” - Mark Twain