The long and short is that they were fantastic. They not only fixed my car quickly and at a far more than fair price, but also addressed my misguided theories on the problem without making me feel like and idiot for them.
I walked in and told them I was on my may home to Colorado with my family and that my 2008 Outback was shaking violently above 60 MPH. The guy at the front desk (I'm really bad with names but thank you sir) said that the tires might just need balanced. I told him that we had a shop try that last night and the problem was still there. He explained that they use a different method then most shops and simulate the weight of the vehicle while the check the balance. That struck me as unlikely to solve the issue and sounded like a way to charge me again for the same thing that didn't work the last time.
After expressing my skepticism on the simple fix, they put the car up on the lift and their Subaru expert took a look. He was friendly and explained that there wasn't any sign of a larger steering or suspension issue and that to him the uneven wear on the tires pointed to them being unbalanced. They did their version of balancing the tires and said they made large adjustments to what they found. The mechanic took it on a test drive at highway speeds and didn't feel any shaking.
I was really grateful that they took me in as quickly as they did but still concerned that it couldn't have been so simple.
Well, after driving the rest of the way home, sorry for ever doubting you Front Desk Guy. You nailed it straight away. Also thanks to the mechanic, you rock.