Currently, if you are viewing a diff that happens to have a bunch of autogenerated files that you don't really care about, site performance is severely impacted.
A current pull request I'm reviewing has a reference.cs file with ~3000 lines of new auto-generated code and a generated wsdl of ~2000 lines of code, along with other programmer code that I actually want to review. This situation basically renders the code review tool worthless.
We've also run into this issue numerous times when we have test files that are in xml (in our case rdl's).
It would be great if the reviewer had the ability to show/hide files at will to improve the site's performance, or some other way to break the diff up into manageable pieces.