I have the same question. According to united.com, "Star Alliance® Gold members, including MileagePlus® Premier® Gold, Premier Platinum and Premier 1K® members are allowed to check up to three bags, each with a maximum weight of 70 pounds and a maximum outside dimension of 62 linear inches." But, according to Lufthansa.com, Star Alliance Gold member get "2 bags up to 23 kg (50.7 lbs) each." So, what happens when I check in with UA but connect to LH?