The project "rationale" has a lot of holes in it.
> Instead of forcing your users to scroll through a giant list of items, they can just start typing the name of the item they were looking for.
Who's forcing? Modern browsers allow a user to type (in lowercase) text to find in a select element while focused and will scroll to an exact match inside of it. It would require some instructions, but deviations of that behavior have been around for a while.
> Because chosen replaces normal html select fields, you don't need to do anything special to make it work for browsers without JavaScript.
One definitely needs to do "something special" to make them work. Limiting options to massively bloated libraries like jQuery and Prototype is a big problem, especially for graceful degradation (impossible with both).
I'd be interested in something that works without a DOM library (definitely not impossible). Support beyond IE 8 would be a great idea as well.