I've found Unity to be a great resource for writing unit-testable code, and tests targeting it. Sadly, not all those unit tests work perfectly the first time (TDD notwithstanding), and sometimes it's not even immediately apparent why they're failing. So I use Visual Studio's debugger. I then see SynchronizationLockExceptions thrown by Unity calls, when I never did while running the code without debugging. I hit F5 to continue past these distractions, the line that had the exception appears to have completed normally, and I continue on to what I was trying to debug in the first place.
In settings where Unity isn't used extensively, this is just one amongst a handful of annoyances in a tool (Visual Studio) that overall makes my work life much, much easier and more enjoyable. But in larger projects, it can be maddening. Finally it bugged me enough where it was worth researching it.
Amongst the first and most helpful Google results was, of course, at Stack Overflow. The first couple answers were extensive but seemed a bit more involved than I could pull off at this stage in the product's lifecycle. A bit more digging showed that the Microsoft team knows about this bug but hasn't prioritized it into any released build yet. SO users jaster and alex-g proposed workarounds that relieved my pain--just go to Debug|Exceptions..., find the SynchronizationLockException, and uncheck it. As others warned, this will skip over SynchronizationLockExceptions in your code that you want to catch, but that wasn't a concern for me in this case. Thanks, guys; I've used that dialog before, but it's been so long I'd forgotten about it.
Now if I could just do the same for Microsoft.CSharp.RuntimeBinder.RuntimeBinderException... Until then, F5 it is.