Anyone else heard the rumours about an 800mm version of the DO? Given my current love affair with the 400, that would certainly be a lens to lust after
That rumour is certainly new; I didn't know of anyone claiming that Canon integrated the 2x TC into an existing design.
But perhaps what you're thinking of is the rumour of a completely new lens with DO, the EF 800mm f/5.6 DO IS USM. That is largely considereda fake.
If you want to keep track of all the more or less ludicrous rumours that have appeared during the past years, check this site out:Northlight Images - New Canon EF Lenses
This is of course a page that wouldn't exist without the Canon 1DS Mk3 rumours page
But they're just that -- rumours.