I use PDFcreator on my Win7 64bit system with office 2007, works fine.
Converting a 2 MB ".docx"-file with my preferences I get a 2.3MB PDF-file. Now I change nothing except installing office 2010. Afterwards I create a PDF from the same file using the same preferences and I get a PDF-file sized 32 (!!) MB.
I assume incompatibility with word 2010. Does anyone else encounter similar problems?