1. In e.g.

http://deadlock.netbeans.org/hudson/job/release69-contrib/jobConfigHistory/?

you can view diffs between config.xml as of 2010-06-07_21-21-32 and as of 2010-06-07_21-25-18 only by selecting File A in the former and File B in the latter. While this generality is useful on occasion, most of the time you simply want to see what was changed on a given date. For that, the best UI is a simple hyperlink next to the "Changed" row displaying the diff from the previous snapshot known for that job (if there is one, i.e. if the plugin was not just installed).

2. In

http://deadlock.netbeans.org/hudson/jobConfigHistory/?

there is no option to look at diffs at all, or even any clue that you can see diffs. You have to navigate to a job to see diffs. (The Jelly form apparently is able to show diffs if a 'filter' parameter is set, but I see no way to set a filter.) #1 would be especially valuable here.