As bad as it may sound, I think you just have to keep doing what you're doing.

I think the potential audience size for Server Fault is larger than that for Stack Overflow; the potential audience size for Super User is practically every human who uses the web. As a result, there is a lot more "noise" already out there on the web for both of these groups -- tons of scattered pages with "tips" for computer use, or half-finished notes written by admins to themselves; put up on the web because, well, why not?

It will take a while for the "signal" from these sites to start to attract more attention.

If and when Super User reaches critical mass, though, ...