I use Firefox, and I've been getting that message for a long time. I've not seen the toolbar on www.google.co.uk at school, using IE6, and the last time I used it was last week.
Its just an advertising pitch for a bit, its only on for a few more days..maybe evan a week or so, just to get more people to download it, its atcuali pretty useful, especially if your in the U.S