I just talked to SQ reservations regarding a SQ/UA reservation and they were quite insistent on reminding me that their baggage limits do not necessarily apply to UAs and that she thought UA's limit was 50lbs. I told her that if you are star gold that UA is also 70lbs. She said thank you and said she wasn't sure and that they have had frustrated passengers and are trying to remind people to watch out.

UA's info is here, and is quite extensive in examples and explanations: http://www.united.com/page/article/0,6722,51146,00.html