Just a tip: to teg a list of checkout for all users, navigate to the root folder of the directory tree you want to check in your workspace using a Visual Studio command prompt.
Then use the TF tool with the following command line:
"tf status /user:* .* /recursive"
When the ".* /recursive" is left out, it will provide you with a list of all check-outs in all workspaces. But mostly this is too much information. This syntax provides an easy way to check for checkout within a Team Project for instance.