I'm pretty much in the camp with Terry on this one.
Yes I understand its tradition.
Yes I understand its supposed to be the gentlemanly thing to do.
Yes I understand your indoors and techincally don't need it.
But I don't see a real practical reason for this. If we're going to say "well we've always done it that way" then I can think of a lot of undesireable things we've just always done as a society for traditions sake that we rightly so no longer do. Other reasons such as being improper, ungentlemanly, poor behavoir is completely arbitrary and without basis IMO.
For example if we lived by Japanese standards, we would all be extremely rude for wearing shoes indoors which is probably a much bigger no-no than wearing a hat indoors. So this comes to the heart of the issue. What makes it OK to wear shoes indoors here and not there? On the same vien what makes it improper to wear a hat indoors?? At least in Japan there is some practical reason in not wanting to get mud/oil/whatever else is on the bottom of your shoe on your carpet/flooring. But who is hurt so much by someone wearing a hat on their dome while knocking back a cold one after the round?
All this being said, I understand when I'm a visitor in other people's abodes or clubs I will respectfully abide by thier wishes. But you can always wear a hat anytime you visit me and its perfectly fine.