Remap or URI Routing or What?

[eluser]mddd[/eluser]
I would say just ignore those arguments. If you don't pay attention to them, no problem right? You could redirect, but I don't really see why. I think it makes your site more robust if it takes arguments even though they don't have any effect.

With regards to search engines: I think if there is a logical page to redirect to, do that. If there is not, show a 404. What I mean by this: for /communities/some-community/non-existing-method you could redirect to the /communities/some-community. That gives the user (or search engine) a page that is still related to what they were looking for. But if www.example.com/non-existing page is called, I would give a 404. If you don't, you would have to redirect everyhing to your homepage and that would be silly.

In my opinion the bottom line should always be: think of it from a user's perspective. If there is an error in the url, what is it that the user probably was looking for? Show that information. Thinking about users' needs will usually be okay for search engine rankings too.