Hopefully there is an obvious answer to this that my brain at 2am is not seeing (I'm basing this on the fact I can't find anyone else with the same problem).
When I press the "hardware/built in" back button on my windows phone 7 none of my bindings are re-evaluating. For example on my MainPage I have a button's "IsEnabled" bound to a bool property in my ViewModel that checks if a value is in isolated storage. In the emulator it starts as disabled (obviously). I then navigate to another page and add the required value to isolated storage. When i press the hardware back button to return to the original page the binding does not get re-evaluated and my button remains disabled.
However if I go back to MainPage via code using the navigate method the binding gets re-evaluated and everything is good.
Any ideas as to why?
The issue sounds like the RaisePropertyChanged method isn't being raised by your MVVM Light ViewModel - if you're binding Get{} accessor of your IsEnabled property on the viewmodel directly to a value in IsolatedStorage, then the ViewModel isn't going to know that that underlying value has necessarily changed.
When you write the value to IsolatedStorage, you can use the Messenger interface in MVVM to notify the ViewModel-in-question that it should fire the RaisePropertyChanged() event for your model, and that will re-bind that property in your view.