I'm currently wondering what the best offhand to pair with a Thunderfury is. I'm aware that Maladath is the best pre-Naxx sword offhand due to glancing blow mechanics... however TF and glancing blows are interesting.

A substantial portion of Thunderfury's damage is nature, and is therefore not subject to glancing blow reduction. Its also a rather weak sword if you seperate out of the physical damage part. The more times TF hits the more times it procs.... so are you better off minimising glancing blows with Maladath, or running a +hit offhand like Puglio?

Opinions? My initial impression is that the effect would be pretty similar.

Forgive me for my noobishness, I've never seen why the Thunderfury itself is not considered an offhand.
Most of the damage comes from the proc therefore not subject to the 50% off hand damage. The only explanations I can think of are that off handing reduces proc rate (which I haven't seen conclusive evidence for or against) or that people consider it a must in the main hand because its orange.

Thunderfury is main hand only. :)

Even if TF wasn't MH only, you hit a lot less with off-hand weapon, and therefore would get less procs over the same timeperiod.