For the past few patches I hadn’t seen much that meant Dual Wielding was viable, but that seems to have changed in WoW’s latest patch 3.3. If you take a look at the Elitest Jerks forum there’s a Dual Wield tanking build posted (Link). There’s also a couple of Dual Wielding DPS builds over at Skeleton Jack’s blog (Link).
Oh and I forgot to add, keep in mind that these builds are viable in the latest patch as of this post which is currently 3.3. That means no promises on what’ll happen in the next patch etc.