Some of the things that I have been using it for on some of our lower level servers (that we do not have licenses for commercial monitoring tools) are to:

verify SQL Agents are Running

verify SQL connectivity

Ping Servers

Send messages on failures of these things

storing all of this sort of data within SQL for reporting later

These things can be useful if you can not afford Idera DM or Quest Spotlight for your servers, since it can give you most of that same inforamation.

As mentioned above we also use it for space tracking on all of our servers (SQL and Non-SQL). WMI is great for that sort of thing.

I have also found Powershell useful if you are the kind of person automated copying/deleting/maintenance of files. It gives a very easy interface for that sort of thing, and once you create the script you can just keep calling the same script with different arguments, which makes it very flexible.

I am always looking for other ideas to use PS for so I would love to see if anyone else has thoughts.