One of the great UI features of FogBugz (in my opinion) is the CSS popup when you hover over a link to another case. I would love to see the same thing in the SO sites. There are many times when I would rather see a popup of a link to another question rather than following the link, or even opening a new browser tab to it. For those not familiar with FogBugz, the popup contains a preview of the content of the page that the link points to (not necessarily the entire page).
For those who don't like the popups, there could be an option to disable them that is settable in the user profile.
Here's a screenshot of the FogBugz popup. I think it's quite helpful as just a reference point. The popup preview of case 13789 appears when you mouse over the Case 13789 link. And again, it could be a per-user option since I know popups are not the most popular things on the planet...
In the preview I think it would be helpful to have:
- Preview of the question and info on the original asker
- Preview of the accepted answer, or if there isn't one a preview of the most upvoted answer or, in the case of a tie, the first posted answer with the most upvotes