With MLBs that support dual channels, and being that the OS runs from RAM, is there a functional difference between 2x1GB vs 1x2GB sticks?

With 2 sticks, there can be small speed benefits if the processor is heavily utilised (lots of video transcoding for example).  Regular streaming to or from the array generally will not keep a processor that busy (unless it's really slow already).  Power consumption can be increased by 2 or 3 watts with a second stick, but again this is mostly only going to be measurable when things are busy. 

 

Personally I would go with whatever you have available or whichever is cheapest, or makes most sense in terms of future upgrades.  Perhaps 1 x 2GB now, but add a second in the future if your needs grow...?

One benefit of two sticks is it makes it easier to troubleshoot. Easy to install only one stick at a time to eliminate RAM as a possible problem.