Google latitude - seeing location?

I've installed google latitude today and made a google email address, It lets your friends know where you are, but its constantly uploading your position through your phone, I have an unlimited internet usage on my blackberry, I think its a fair usage policy of 500mb, if I leave it on all the time will I go over 500mb if its constantly uploading? I don't know how much it takes to download maps on to your phoneGoogle latitude - seeing location?
this clearly looks like a question for google to answer :)

lip balm