I assign work-items to user-groups in TFS. Lets say, I have a task assigned to the group [Devlopers]. Now I want to setup the Team Query \"My Tasks\" so that every member of [De
You can't set the field "Assigned To" to a group, TFS only support setting a valid user.
You can change the Work Item Type definition to remove the constraint "validuser" and save any kind of text inside the field but don't expect to get groups that way.
This is a "complaint" many made to Microsoft for years but it stays as it always have been: no group.
You have to change the WIQ (Work Item Query) to use other fields to get the result you want. Looking at the example you gave I strongly encourage you to scope this query with the state, the area and iteration.
I've been wanting to do exactly the same thing, and found the following "work-around" which enables some of the functionality as you want.
For this to work you'll have to either:
bare in mind this is after you have altered the work items to enable assigning to groups. You'll then create a query for each of those groups as you need to specify the group name.
What I did was create a dashboard for each team, and on the dashboard had any "todo" items / change requests / tasks / bugs / etc.
It isn't possible to have a "is in my group" filter, unfortunately.