Finder Enhancement - Customize Icon for filetype Is it possible to customize the icon that's used for certain filetypes in Mac's Finder?

I have a folder with a bunch of .mobi files. In finder, If I view by icon or coverflow, it just shows a generic .mobi icon for all the items. I'd like to instead see the covers for each of the books. PDFs seem to already do this by showing the first page of the document as the icon.
This works for PDFs, and many other types of documents because the OS X Quick Look Framework can natively read those filetypes. All other filetypes get just an icon rather than a preview. Best guess is that that framework doesn't support .mobi files.

Without native support from Apple, your best bet for .mobi (and any other unsupported file format), is to look for a plugin. A quick Google search turned up this. I don't have any .mobi files to test it on, but it's worth a shot.

Generic QuickLook Plugin installation guide here. Good luck!