The Washington Post reported earlier this week that the new umbrella site for applying for U.S. government funding, grants.gov, uses electonic forms that won't work on Mac. A client program which reads and edits the forms only runs on windows. The government is scrambling to get this fixed, and the NIH will delay the requirement that the big R01 grants are submitted electronically (this affects me personally!). However the smaller NIH grants apparently must be sent via this program.
I was using the handy technorati feature that the Washington Post includes with its articles, and I found that Suresh has already written about this, including referring to an open-access workaround for Mac from the University of Wisconsin. If you're in grant-writing mode, this may be a solution.
This isn't a simple issue. Have a look at Behind the Curtain for electronic document issues, creating an acceptable umbrella standard, and some other history.