Right now, GitLab.com is slow [0] and the interface is a little bland [1]. The features to support open source projects are there (I'd say, but please let me know what we miss), it's a matter of iteration before we should really be the preferred option.
And it would be great to decrease the content block's width to something like 75-80%. Just like GH, HN, millions of other websites, and even BB.
I have two suggestions regarding discoverability: when I visit a developers homepage I normally want to see his bio and his projects, not his latest commits (which is the current landing page). I assume the former is also more cache friendly and less expensive to generate for gitlab.
Furthermore, on github when I find a great developer I always look who they follow and sometimes also who follows them. This together with the star system is a great discovery tool (although it also fills your start page with endless commit messages from other people). Something similar to this but more automated and less noisy would be highly appertained.