Well I have now used the new IOS on Unix (IOU) based virtual labs from Cisco for the past three days for my CCNP ROUTE course. So far I give the lab environment itself a B+. Being that it is real IOS, the routers are full featured. Unfortunately the web interface surrounding the IOS instances is still a bit clunky. I would like to see tools to save and load configurations via text files. I would also like to see a better L2 switch implementation. The switches in the labs were unable to be setup for more than one vlan which meant the topology wasn't really setup correctly.
The lab exercises were where things really broke down. Because you can't change the wiring configuration or the number of devices, you have to rely on Cisco to build the appropriate topologies and initial configurations to match the lab guides. Unfortunately they apparently never reviewed the lab guides for the OSPF labs in the CCNP course. None of those labs was configured correctly which caused a lot of extra work before being able to even start the lab you were assigned. I guess that Cisco was trying to mix TSHOOT with ROUTE. Because of this I have to give the lab setup a D (the EIGRP labs were done correctly).
Being that this lab environment was just released recently, I'm hoping that the quality improves quickly as people report the problems.