I'm surprised at that amount of active checks for a web app. What are you checking really - things like responsiveness, or more correctness? And do you include only the webapp checks, or also the underlaying system.
I'd expect somewhere around 20-40 checks for the system itself, so it looks like a reasonable number for a single app/deployment. Then again, I'm a passive monitoring fanboy.
Actually I think active is probably the wrong word, so changed in the post, but to answer your question:
It's a system based on multiple web services and run across multiple hosts, and I've included all system checks in that number. So we have checks for:
* ping, ssh, disk, load, network io, etc.
* error rates from request logs
* request rates (warning on high values)
* smoke tests for key functionality (i.e. does the search engine return results, can you complete certain forms, etc.)
* connection tests from relevant hosts to relevant services or databases
I'd expect somewhere around 20-40 checks for the system itself, so it looks like a reasonable number for a single app/deployment. Then again, I'm a passive monitoring fanboy.