Now, I am an avid fan of WordPress, and have built dozens of sites on the platform over the past 6 years. It's quick to build on, easy to learn and fantastic in every area.... almost.
I think the one area that the administration area is really missing an opportunity at the moment is in it's slow load times when there is a large number of pages/media/custom post types etc. to filter through and display. When searching through images, or trying to find a specific page, this whole process would be significantly sped up through the use of Ajax filtering.
It's in use on some areas of WordPress already (such as when linking to a page), so I'm still suprised when such a small amount of areas uses it. The new media area in WP 3.5 may do, but still not in the 'Media' tab!
Please like if you want this implemented, hopefully we'll see it in an upcoming release :)