We don't have a formal per day limitation. There is rate limiting per
minute and per hour but it varies depending on the load of the entire
system. If you're refreshing once per minute or two that should be
fine. (and in reality most users aren't modifying their portfolios
every 5 minutes).
There used to be a 200 transaction total, I believe that has been
raised significantly now.
Terms and conditions are:
http://code.google.com/apis/finance/api-terms.html