You get better compensation when it goes wrong if you are a business and in my experience better call out times too. It also means you get listed int he phone book as a business and get your free yellow pages entry. Not sure how easy that is so do if you are not a commercial customer.
thats the one I couldnt think of - certainly with BT the broadband tech support and resolution is light years ahead of the residential product.
pm me with the price and details of what you are being quoted - I have access to bt wholesale broadband prices so can let you know if its reasonable.