I have no clue what rails application are on that server (I am just using the wiki and am new to everything around here), the only thing I know is that ruby & rails does not scale very well.

So when looking for causes, you should probably consider the possibility that the site has just become hugely popular and that this is just causing too much load. if that is the case, then an easy fix (that does not require rewriting rails stuff in some other framework) is to buy lots of servers :P