Thabks for a good article. In my previous company, I used to handle near about 300 db servers with data aggregate to 13+TB. I was assigned o build the production dba team. During the team build, the projects used to grow further so everything was difficult initially.
We used a 3 tier monitoring system, with a third part tool moniotoring the application response, round trip time, uptime and numerous other things. Any fall in the response time used to send us emails and pages. The next tier was a tool that used to check the server side - cpu, disk space, port checkings etc. The next level was our custom written wmi, SQL DMO scripts. DMO really helped in doing almost all types of audits. I would recommend using SMO (DMO being deprecated in 2005) and write our own custom scripts to check virtually everything.