Maybe we can have PasteBin and GitHub Gists embedded directly into CodeReview.
Given that each Gist has a unique number maybe it could be.
[gist NUMBER HERE]
This would simply translate into
<script src="https://gist.github.com/ <<NUMBER>> .js"> </script>
I am not familier with PasteBin but there should be one for that too.
I can't speak for anyone else on this matter, but if the code to review does not fit within a post then I probably won't have time to go over it. We can already fit several hundred lines of code in a post.
I thought about using your suggestion to provide "supplementary" code but think that would end up encouraging the undesirable behavior of people requesting reviews of entire projects and not providing enough context within the question itself.
I don't think this is a good idea. It's doubtful that it increases efficiency much, since you still have to cut and paste a link. Also I believe it would encourage people to post more code, and we don't want code to be too long. If a piece of code is that log to begin with it's probably doing too much anyway. Longish is fine, and I am against placing an arbitrary limit on a post. However, if you post too much code people won't really want to wade through it and both the questioner and the site loses.
EDIT: As previously discussed, not everyone can get to pastebins depending on firewalls, etc. Embedding code will still suffer from this issue.
