Recently I have come across Microsoft Team Foundation Server Service preview. The service is currently offered for free and supports both TFS and Git version control systems. So I have signed up :) The only thing that reminded to make use of it was to connect PowerGUI to the service which turned out to be quite trivial. So I will show you how to do step by step:
Some basic documentation on connecting PowerGUI to TFS is provided on the PowerGUI Wiki. To be able to connect to the TFS Service you need newer MSSCCI Provider installed. Both 32-bit and 64-bit version are available on Microsoft pages, but my PowerGUI x64 seems to detect only the 32-bit version.
When you have downloaded and installed the client you need to restart your PowerGUI editor and go to Tools > Options… > Version Control and select Team foundation Server MSSCCI provider as your current provider.

Then, in the main editor window, go to new Version Control menu and choose Get files from Version Control. New windows appears, where you can choose which provider you want to use. You probably have none there yet so you need to add one by clicking Servers… > Add… This will get you to this menu:
Add new TFS Service to PowerGUI.
Here you have to specify URL to your TFSS account followed by “/DefaultCollection”. Click OK and you should be prompted to login to your Microsoft account:

Logging in takes few moments and then you are hopefully presented with this window:

Just click Cancel to return to the selector:

Click OK here and you are good to go.

In the next step you need to choose local folder to store the data and also choose server path to the project you work on.

Next you need to choose file you will edit, I have chosen to name it hello.ps1.

If you are yet to create one go to your browser, navigate to your TFSS web page and create new Team project.

Now you have your file opened and you can CheckOut, make your changes and CheckIn.