Looks good.
Do you have plans to introduce the "template" and/or "group" concept?
e.g. I have a template called "Windows" Apply it to my windows servers, they get defaults applied for thresholds. Eg. Cpu is set to 80% warning, disk is set to 75% full, certain services are checked, etc.
Another template called "Apache" It gets process checks for http added to the host...
My host called win-apache.example.com gets 2 templates applied to it. You can also override default settings for each host.
Concepts from bbconfigure on deadcat ;) Makes large scale management much easier.
Craig