Using the Tag All tool to quickly Tag all untagged elements in your model is a great way to get Tagging information onto your view. You just need to go and fine tune the position of the tags after they have been automatically placed.
When you are trying to Tag All rooms, there can be a bit of a lag when Revit queries the model to determine the rooms. You can give Revit a bit of a helping hand by having all the rooms selected prior to clicking the Tag All tool. This should speed up the process.
Just highlight the model and filter out everything except the rooms. Then select the Tag All tool.