One area where a lot of smarts are needed needed, for example, is making sure that you're intelligently routing encrypted packets to the right machines without reverting to a broadcast to every router, switch, and machine in the DC.
I've also heard a lot about people running brand new untested protocols (like TCP replacements) right alongside traditional protocols through SDN.
I'm probably going to do a much worse job of explaining things than the guys who presented at the Open Networking Summit [1]. I highly recommend giving the keynotes a listen.
[1] https://www.youtube.com/user/OpenNetSummit
Edit: I do think this relates to SDN more than a traditional router/switch OS, based on the comments about "traditional and programmatic, declarative control plane." Either way, though, the link above is definitely good stuff.
It provides open interfaces to interact with the switch through several means like OVSDB, REST API ... or CLI. OpenFlow is not supported yet although will be in near future.
Since it's open source, it also gives you the opportunity to run other agents in the switch control plane ... which is hardly possible with IOS or JunOS.
I am going to guess large high throughput switches and some degree of software defined networks that knock putting your printers on one C-network and your servers on another into a cock hat
Apart from raw power, is there some way I can reconfigure my network without moving a cable that I previously could not?
(It's late, so just to be sure, I'm not trolling)