From the press release:
To read their personal or professional documents, Kindle customers simply email PDFs to their Kindle email address or move them over using a USB connection. Customers that prefer to have their PDF documents converted to the Kindle format simply type "Convert" in the subject of the e-mail when sending documents to their “@kindle.com” address.
Was the "Convert" option already available for the Kindle DX?
The Kindle DX does not reflow PDFs, the Kindle 2 probably needs to include reflow for this to be practical. Since Amazon is using Adobe Digital Editions, this is certainly possible.