Unfortunately that doesn’t work in the current release, we just added $User as a merge variable in our dev version. In the next release you’ll be able to do {{$User.Id}}. However you can achieve this currently by creating a Model on the User object, e.g. called “RunningUser”, to request the fields you want, and have a Condition where User Id is User Id of the Running User. Then, you can use Global Model Merge syntax to get at the user’s Id: {{$Model.RunningUser.data.0.Id}} {{$Model.RunningUser.data.0.FirstName}} {{$Model.RunningUser.data.0.Username}}

Thanks Zach, good to know it wasn’t me losing my mind.

Note for posterity:  All global merge values are listed here: http://help.skuidify.com/m/11720/l/187263-global-merge-variables-functions