Assigning __proto__ - good idea or bad?

What is the downside of setting Object.__proto__ on an object? In my case we pass objects using the web worker postMessage() and when we receive the object passed, it has all the data but the methods have been stripped off. Setting __proto__ restores that. It seems like assigning __proto__ is a natural for this case.

The alternative is when objects cross in a postMessage, we create new objects using copy constructors. We pass across a boatload of objects in each message so this adds up in terms of execution time re-creating all the objects and the memory hit of duplicating all the objects as well as the garbage collector then has more work to do.

??? - thanks - dave