While it's not the grand opening of the Kindle app store or anything, a developer decided to write an app for Kindle 2 that converts .pdf and .epub docs to Kindle's beloved .mobi format.
The developer, Jesse Vincent, swears he didn't "hack" the new Kindle—rather, he wrote a "package" that happens to run on it. The thing doesn't crack DRM files, it just converts specific unprotected files on the fly—from PDF and ePub to Mobipocket, so it feels like they are supported by the Kindle 2. (Not, alas, the first-gen Kindle.)
As Jesse says on his blog:
Savory installs a small program which runs on your Kindle and watches for new files in the 'Documents' directory with names ending in '.epub' and '.pdf'. When the system notifies Savory that a document has shown up, it wakes up and runs an open-source file conversion program called Calibre. Savory also updates your Kindle2's browser configuration file to tell it that the Kindle can now handle .pdf and .epub documents.
That said, Jesse isn't sure what he's doing is totally kosher:
Does Savory void my warranty?
I don't know. If you're not comfortable with the possibility, do not install Savory.