It's only been about a week in closed beta but the Source Filmmaker has now opened up to all Steam users. If you felt hard done by for not getting an invite before, shed your disappointment and go download the Source Filmmaker right away.
Valve have also put together a SFM Steam community page for people to rate SFM creations, using the Steam Workshop infrastructure. To ease up on the amount of 'Meet the Heavy' variants released so far, the assets for 'Meet the Engineer' are also now available for everyone to play around with. Have *sneeze* fun with it!