From a storage and memory perspective, 11g is great. We also tried to install 12c on our machines, but we weren't happy about it because there were two version of it and we weren't ready to use the required plugins. We'll go to 12c next year, but I'd like to know whether we can go straight to 13c, which is already out.
Improvements to My Organization:
11g has helped increase the performance of our database. We're also able to maintain it easier and better.
Room for Improvement:
It's really not very user-friendly. Once installed and set up, there are still a lot of other steps we've had to take to get it functioning the way we want and need it to.
Deploying it required a lot of customization steps.
The stability is better than with 10g, in our experience with it.
The scalability is OK, but now that we're pushing 30GB of data per hour, there are problems with applications at the OIS level not handling the data correctly.
I performed the full setup myself but winged the rest. I had problems with the patches even though the upgrade installation went well. I spoke with DBA's in other companies and they had no problems with the patches. I still haven't come up with a solution.
It's a good product, better than older versions.