Just as an addition to tcharlie,
At a recent seminar I went to for wildfire I was shown the same thing, there is one great big drawback though - they are just 'dumb solids' ie. all your design intent through you model tree is lost.
You may as well just export a step file and re-import it into an earlier version. Basically your model will come in as a single feature block, or if its an assembly, an assembly of blocks. I'm not too sure about what happens to assembly constraints though.
I would love to be wrong on this though, so if anyone knows otherwise lt us know!
Cheers
Hayden