Servo is now in Early Access! If you bought from Stardock or another non-Steam vendor, just plug your key into your Steam client (Games -> Activate a product on Steam) and you should be good to go.
As always, you can retrieve any keys associated with your Stardock account here: http://www.stardock.com/support/productkeyretrieval
Now go forth, and blow up some aliens!
Founders should have gotten an email with their Steam key for the Servo Founders Alpha. As always, check your spam folder.
Alternatively, you can log into your Stardock account and go to your Downloads page, where you can always find all the keys for all your Stardock products.
You can also use this handy tool to have all your Stardock keys emailed to you: http://www.stardock.com/support/productkeyretrieval
As with all Steam keys, choose "Activate a product on Steam" from the Games menu within the Steam client and input your key in the dialogue that pops up.
If you're having any issues downloading or launching Servo, please contact Stardock support at http://support.stardock.com and we'll get you sorted out.
Thanks for your support!