I think it would be a waste of time for the creators of the site.
43 Things works very well as a site on its own, but combined with facebook, what would be the added advantage?
If it’s to make 43 Things more popular, then just tell your friends about it. The application wouldn’t be very different from the mother site, so those people with 43 Things and facebook would probably use them separate for convenience.
I’m quite happy using them separately :D

