I use sourcegraph occasionally and mostly rely on Gihub search. I wish the search has all those advanced refinement options that grep & Sublime Text search has. Some examples would be to use regex, search a word within a scope of lines, search within search results etc. Additionally, it's very useful to be able to sort the search results by stars/forks. Sometimes I just want to see how popular projects have implemented a certain feature. A keyword based search isn't enough for that.

I guess these features are very expensive & slow to implement but it would be super useful if it can be achieved. Source code search is for geeks so it is probably fair to say that a truly advanced & complex interface won't turn away users.