I don't know of anyone who uses Gitlab. We use Github at work, and I know several people who use Github at work. In terms of features, I can't think of anything that Github doesn't support. If something is missing, you can always find tools/services that integrate with Github.

That said, I am quite surprized that Gitlab is growing so fast. I would be curious to know what is the source of most of their revenue. Are they targeting a specific cohort of users, which Github is not able to?