Ask HN: What problems do you have with GitHub Pull Requests?

My team is considering moving to GitHub from BitBucket. I'm trying to do some research to find criticism of the PR mechanics on GitHub but my searching is weak or it's hard to find.

We are going to dual-remote it for a bit and actually try out the GitHub and do some PRs there so we'll get firsthand testing. But, GH does offer a lot of functions that BB doesn't so until I know about all of them, it's hard to gauge how the full GH environment will suit us.

So I'm looking for some folks that really understand GH to comment on how to do effective PRs with all that GH has to offer. Anyone know of a good resource or willing to provide some commentary?