The 10G uplinks and pinning, FCOE (and now with the new Nexus' you can do multihop FCOE if you are really gutsy).
Once you wrap you head around the idea of a logical server profile (which isn't that hard), they become very simple to work with. Well you will also have to expand you knowledge base to learn a little about storage and networks (but not that much).
The Palo cards are actually one of the coolest things anyone has created in a while, virtual PCI-e, its pretty cool.
As for whether they will stick with them or not, my thoughts are this, virtualization is dropping switch port counts in the core of your datacenter, Cisco has a choice, they can watch their revenue shrink, or create something like UCS and extend the data center surface area generating revenue. I think they will stick with it because they have to. AS for the price, list is high, but they actually give better than normal discounts on it (they explained the reason for this, but i don't remember right now).
As a point of comparison, we also purchased some HP c7000, they are really pretty crappy, we have had a lot of technical problems getting them working and frankly for every 16 blades you have another mgmt point, and a whole new set of uplinks and chassis infrastructure. HP really phoned it in.
Besides the c7000 there really isn't any competition.
I am sure this sounds a bit fawning, but we have had them for about a year, and I still think they are amazing ( and I am normally very cynical about new stuff, curmudgeonly even).