What Are Typical Load Averages for Servers?

Jon Hill asks: "I'm curious to figure out how to guage the performance of my servers and know at what level of usage I should think about hardware upgrades. 90% of our servers run Linux and various services standard to Linux such as sendmail, samba, DNS, etc. One of our main servers (router/firewall/sendmail/spop) has been running with a load average of .5 to 1.5 regularly. It supports 200 users and is an SMP Intel machine with 2GB of RAM. I'm not sure if it needs software/kernel tweaking or hardware modifications and I can't seem to find any reference information. Suggestions?"