Here's one I'm ashamed to admit caught me as I was finishing up work this evening, it's been a good few weeks since I've gone near wpf/silverlight given I was on holidays and spend my time playing with WF4 and MVC2.
Anyway in screenshot below.. vs2010 .net 3.5 sp1 I was binding some data to a datagrid.
I omitted to remove the offending closing xml comment you can see in the xaml "-->"
And low and behold the binding breaks down without any prior warning,,,, infact my object collection is totally ignored and the "-->" is passed to the binding, I know this because I removed the binding paths in the columns and was presented with "-->" in my grid...
Just an interesting one to keep in mind.. If you're like me, u couldn't switch off the computer this evening until this peculiar behaviour was explained..
Maybe it will save you some time if you come accross it.