Just upgraded to Quicken 2012 using Windows XP. I was successfully able to merge my individual file ((including all account types (that I have), such as, checking, savings, etc. except for investment types)) into my girlfriend's (wife's) file.
I used the Quicken Transfer Format (QXF). Clicked File, File Export, Quicken Transfer Format (QXF) and followed the instructions. I did create a new, separate master destination file from my girlfriend's individual file because I am paranoid.
Process was faster than it took to download the software upgrade. Repeated about >10 pop-up prompts telling me that I had a duplicate category. Did not tell which ones and only let me click ok. Also, after the duplicate category pop-ups it had a series of <10 pop-ups asking "Is this existing transaction in account X the same as the transfer you just entered?" Did not show me any transactions I just entered, but did give small details about "this transaction" (date, payee, category, amount). I answered no just in case because I could not see both transactions.
Still have to review and double check every thing, but balances were correct and there appears to be nothing strange or frustrating. Probably took me longer to post this than to do the merge.