hey I used to use "invisible text" because I saw many other sites using it and their page rankings shot up to the top. I started using sitemaps but it basically gives google a better blueprint to look at whatever you've got sitemapped. So I got an email from them regarding the invisible text LOL. luckily I fixed it, replied to the G's, and all was good. Sitemaps are good for stats and keeping track of search queries (that's what's been useful for me) but it basically tells google which pages on your site to examine more closely FYI
Question, if Google decided not to use CSS or on-page HTML <font> formatting, wouldn't the text show up anyway? My CSS validation checker picks up on this instantly. Don't you think Google does something like this?