For example the change formats dialog for tips. You can scroll around inside the 300px wide dialog box but this is far from ideal.
Another example is in Views, I have 2560 horizontal pixels to play with and I have to scroll horizontally to see all table settings. If I tab around then it's very easy to get very lost almost strait away, for example focus can go to a checkbox but the label is hidden outside the field of view (you have to scroll to see the label).
1) this is usable and not entirely broken, it works. I'm not sure if this is a bug or a feature request.
2) but it's far from optimal and dialogs accessed by a lot of people, e.g. the change formats dialog on tips, should work a lot better - 300px restriction feels very artificial and rather out of step with our modern elastic/flexible web.