UPDATE: The new format may just be a compressed .gpx file (speculation, but it makes sense). Also, apparently the new Oregons will support .gpx files:
The Oregon can hold an unlimited number of geocaches and supports GPX files from OpenCaching.com for downloading geocaches and details straight to the unit.
UPDATE 2: Read our hands on Garmin Oregon 650 review.
When Garmin announced the new Oregon 600 series, they mentioned the ability to load a nearly unlimited number of geocaches: read more