If you plan to take any of the Microsoft certifications you will need to know PowerShell commands. If you work with the product and use PowerShell this is easy. If you don’t work with the product or you only use the GUI, you will have a hard time with the PowerShell commands on the exams.
You should also note that there are different versions of PoweShell for different Microsoft products. For example Microsoft Exchange has a special version with commands for Exchange.
Here are a few resources to help you out:
Windows PowerShell Survival Guide
Channel 9 Videos