Hi there, I picked up the X10 lens hood with adapter for 52mm filters and it works OK. I only use a polarizing filter occaisionally, since the hood itself protects the lens from coming into contact with anything if I'm reasonably careful.
My local camera shop has some very knowledgable folks and one mentioned that you can actually get a 40mm (or maybe he said 42mm?) filter to fit, but the thread pitch is slightly different so you have to force it on a bit.
Actually though, the adapter that comes with the hood is only a sliver of double- threaded metal ring. So, it works as an adapter for 52mm filters and then you can put the hood back on over the filter(s) – effectively giving you double the protection.
This was all definitely not clear to me at first, and I'm still not sure I understand the reason for the adapter other than an extra $60 for Fuji.
If you get that accesory, you also might as well splurge for the thumb rest and shutter button extension. At least for my hands, they make the ergonomics of the X-20 just perfect.
Hope that helps.