Selectively importing other people's pull requests in your own Github fork

Given a generic open source project on Github that I have forked, is there any way I can find a pull request, submitted to the original branch, and choose to "import" it in my own fork (given that the files should be diff-compatible) so that it will be applied to my branch?

Yes. Here's how I would do it:

1. Fork the repository to myaccount/project
2. Clone myaccount/project locally
3. Use git remote add [remote name] for each of the remotes that have fixes you want to use.
4. Run git fetch --all to download everything
5. Use git merge --no-ff -m [remote-name]/[branch-name] to merge in the changes from each Pull Request that you want to include in your fork. --no-ff creates a merge commit for audit-ability and -m let's you specify the message in your editor (so you can include a link to the Pull Request in your merge commit).
6. Once you've made the merge, you can use git push to update your fork on GitHub with the various Pull Requests that you've merged in.