I like the whole WMI concept, and I could really make use of it under Linux (in some scripts). Is there something like that for Linux systems?
Take a look at the /proc interfaces. You can get a lot of system information there. There are also many excellent utilities for gathering system information. The sysstat packages are always one of the first things I install these days.
Edit: You can always query SNMP as well. There is a lot of information exposed by default.