i'm glad that google translate is adding farsi to its repertoire.
but i would also advise caution. google translate for arabic can sometimes be really bad. i've been slowly working on as post for the past few weeks about google translate-arabic. i cooked up a test for the service to see how it does translating arabic to english. i don't want to spoil the ending of that post, but let's just say that it has done really poorly. because arabic isn't written with short vowels and thus a lot of words can only be assigned meaning by context, it 's particularly difficult for a machine to translate. farsi is written with a modified version of the arabic alphabet, but beyond that i have no idea if it has the same problems.
UPDATE: mark liberman from language log does a preliminary test.
UPDATE2: another test, this time by cyrus farivar.