Friction in the free hub? I have noticed there's some friction in my free hub on the TCR - when I pedal backwards slowly, I can get the rear wheel to roll backwards (while on the stand). This strikes me as a bad thing - means when I'm coasting on the bike, I'm losing more speed than I should be.

Is there anything I can do to fix this? Is this something I should take to my friendly LBS and have them take a look, or is it something I should be able to handle at home?
My Ksyriums do that, and have done for the last 5 years.  They still work fine, so I wouldn't be worried about them breaking.

I have on a couple of occasions taken the hub apart and cleaned an re-greased the palls and all bearing surfaces.  This seemed to reduce it slightly.

I would not recommend any changes to the internals of the hub, other than cleaning and lubricating.  The consequence of a hub failure at speed are quite bad.  The amount of drag you are experiencing is quite small.  It's not worth risking that crash for that tiny gain.

If you are racing, and that tiny amount of drag really is the difference between win/lose (or, as in my case, between being dropped and hanging on the back. ;-) ) then you might consider second "racing" wheelset.  If you do that, I recommend ceramic bearings.