InfoPath uses IE for rendering to the best of my understanding. In the past, I have seen on machines where the IE font size is set high the fonts are rendered in a larger size on the form - this was back on an IP 2003 form that I saw the issue, but it seems to me that it may be worth ruling out - it is a easy thing to check, after all. From the View menu (if your menu bar isn't showing, and you are using IE 9, hit the Alt key), select Text and change sizes. What happens to the form rendering? I just tried this on my Win 7 / IE 9 / IP 2010 machine and when I increased text size to Largest, the first items in my form used a much larger font than they were set to in design mode.