Old thread, I know, but I have an anecdote to add...
I had been on 10kIU/day of D3 for months now. I found when the weather turned cold that my lips would get UNBEARABLY chapped. So I am currently off D3 (though there is still 600 IU in the mineral supplement I take). Next supplement order that comes in will have some 5kIU D3 and we'll see if that makes things any different.