You are better off just taking a cash promo.
Locally for SF, we can choose between SBC/Yahoo DSL ($15/mo for 12 mo.) or Comcast (Cable) ($20/mo for 6 mo.)
If you sign up at Circuit City, you get a free modem plus $75 rebate. That's like getting service almost free!
Compared with earthlink ($40/mo for 12 mo. contract, all CS now outsourced to India) it is a no brainer.