Got the new Sto-Fen OmniBounce for the 600EX-RT last week (ordered from Adorama
, now B&H
has them, too). Fit is very snug - tighter than the ones for the 430EX II. There were early reports that the older one for the 550EX would fit, but I wondered about the gel sensor. On the one for the 600EX-RT, there's a little notch for the gel sensor.
The flash with the Sto-Fen mounted is too large for the Canon pouch (barely - the velcro closure still overlaps by a couple of millimeters), but it's a perfect fit in the Lowepro Quick Flex Pouch 75 AW.