Github search is fine, do not get me wrong. But this is like telling someone lamenting on the hypothetical end of Google search: "Just use the search function in Facebook, you don't need more"
I'm pretty sure Joel Spolsky and Jeff Atwood, and probably a lot of other github employees, lurk around here... if you harp on it enough they'll probably make it happen.
My primary use of Google Code search was, searching for this rare function (like a POSIX one) whose man page I can't understand and is largely undocumented elsewhere. I would often try to understand how other projects are using this function via internet-wide code search. :D
While Github is great, I think it still hosts only a small fraction of all the code that is public.