Not sure if this is still the way you're going but, taking into account your comments on performance, surely a lot of NH code uses private variables and not auto-properties... one advantage being you can apply business logic to the prop before you access the variable.
It seems a little restrictive to apply this to auto-props only. Also, on the Ghost properties thread, again I'm sure I fully understand, but there is code out there that uses interface based proxies for entities (e.g. those interfaces already existed to abstract away the domain layer). A useful feature like this should try to deal with those cases as well. IMO
