That's why I prefer asking for any links to their work online, whether it's on github or elsewhere. And I suspect most others who ask for a Github ID would not mind a sourceforge link or whatnot.

I ask for this before the interview, not as a way to filter out people with no work available online, but mainly to gauge their coding abilities so that I know how much I need to cover that in the actual interview. If someone happens to have a great Github profile, it just means that I can skip most of the coding part of the interview and focus on other things.