Performance metrics for network admin

I'm the Network Admin for a small company (about 30 people) and management wants me to develop some metrics by which they can measure my performance. What do you suggest? Where can I look for more info on this nebulous topic?
I would suggest starting simple. Create a database and keep track of how many technical questions you do a day/week/month. Also, you will want to keep track of all technical changes you make within a day and show them detailed reports on the number of changes you make. I think the best metric to judge an Admin by is System Uptime. You can download a freeware program called uptime and install it on your systems. Since system uptime is critical to most business success I would suggest using uptime as the most important metric. Create detail graphs and beef yourself up.