The SMP suite is great at what it does, but it can be very complicated to learn how to get it to do what you want. It's a beast! However, when you learn how to the things you want to do, it comes as second nature and you complete them like they're supposed to be done that way. A lot of these things are done to be able to be completed a number of different ways. Take Patch Management, you can deploy patches automatically, via Jobs, or via the "Start Software Update Cycle Now" link in the SMP Agent!
Overall I would say that we have been very happy with Zenoss. It has been a great server monitoring tool. There are certain aspects that we would like to expand into, such as Capacity Planning, Network Performance Monitoring, and log analysis. We have coupled Zenoss logs with Splunk for external log management, but would like to start using some of the built-in analysis tools.
The SMP solution is a beast. Each piece is complicated in itself let alone how everything ties together!
There is plenty of documentation online on how to perform a specific task, but you need to pay attention to what VERSION the article is written for. I've been halfway through implementing something only to hit a roadblock since I'm running a newer version and the option the article says to click on doesn't exist anymore...
Being able to report on the majority of things you want all from one interface, makes it really easy to get the results you want.
Because my employer didn't provide training, it took working with support, reading technical documentation, and just playing around on my own to learn how to do certain things.
I've had a lot of help from the SMP Support staff and they're great people and very helpful!