We are very happy about zabbix and we use it inside many company processes. The only problem that we have is about extend (or integrate) zabbix inside these processes. When we need to manage zabbix using api we need to study all the docs, find the right way to start the process to achieve the right data (like host name, or trigger status etc) and code everything from the scratch.
This is because you use JSON-RPC to expose ws that have all the features but lack of service description... I think that a good feature can be to migrate from JSON-RPC to JSON-WSP that have everything of JSON-RPC plus attachment support and service description by design. (you can read it also on wikipedia: http://en.wikipedia.org/wiki/Jsonwsp)
With this feature we will able to pass to our IDE only the "wsdl" url and our IDE will create every method to call api for us... Less time and more comfortable