I had to remove a number of plug-ins because they screwed up the theme layout. When designing and coding a plug-in that is intended to add a display of somesort to a Word Press blog plus, if possible, include what's necessary to insure the theme adjusts to the inclusion.
For example, I installed a search plug-in meant to add in searching the forums and codex. The search field sat right on top on my user name etc. on the admin pages. Not a good thing. At the least a bit of code to add to the admin template where the search form would go would be a good thing. This last would be a good idea for any plug-in that adds a display of some kind to a template.