Yes, WF on both hands. Although, I have seen a few pretty good shamans with Flametongue on a 1.5 speed or faster OH do some serious damage in PvE.
For dual Windfury the key is to make sure the Off-hand is as close to 2.6 as possible so it won't "steal" WF procs.
I've actually been toying with an insane Haste-gear set and with double goose procced, Drums of Battle and Blust I've gotten swing speeds of 1.18 (Looky Ma, I'm a rogue!). At that speed, it doesn't matter what hand procs, LOL, everything gets torn to shreds. Good times.