Hi David,
I'm glad you're enjoying Method!
The Gmail Gadget will appear in your Gmail account when you open an email. It will look at the incoming email address and find the associated customer or job in Method. If the customer or job you are looking for has a different email address in Method then on the incoming email, then the gadget will not show that job automatically. However, there is a built-in search feature on the gadget that will allow you to choose any customer or job that you wish. See the screenshot below.
We have a few articles in our Help Center that you can find here. I recommend reading through these to get a better idea of what the gadget can do.
Hope this helps to answer your questions! Feel free to post back if you need to.
Jason