We are coming up against this GBBO recently. Apparently mostly organised by Google we are hearing MANY reports of it being useless for any kind of reasonable business use (no real email, rubbish templates, 0800 number not recognised and so on). If you need a web site I'd rather you used www.my-free-website.co.uk than sign up for something that MANY businesses are realising isn't really fit for purpose. You've been warned but try this link for a LOT of issues:
http://www.google.com/support/forum/p/sites/thread?tid=0beeba463f879b7b&hl=en
And this massive list of complaints is hosted by Google!