The reason why I loved mame32, back in 1998, is that it used what would today be called an "iTunes-like" interface. It made the game library the main interface of the emulator, and you could easily sort, filter, and search for any game you wanted to play based on a nice graphical interface to an organized ROM database.
The MFC Windows-esque Single Document Interface style GUI used for most emulators is simply not the ideal interface for a video game emulator. Mame32 (now called Mame32qa) realized this early on: http://img522.imageshack.us/img522/9638/mame322fz.gif
There was a for-pay Famicom emulator that had a similar interface, and instead of showing a screenshot in the righthand pane, it would simply immediately load the game and show its title screen.
Taken to the extreme, such an interface could provide box scans and manual scans, in addition to the typical screenshot of the game itself.