If done right, it can be great.
In Québec, Canada, two large companies (Bell and Vidéotron) had a monopoly on broadband. A few years ago, a 650k access was about 30-35$ (including modem rental, all fees, with a yearly contract).
Now, Bell is forced to share it's network and small companies can "rent" a dry loop (a phone line that cannot make phone calls) for 8$ a month.
Bell support to those companies was bad (read: non-existant) in the first few years, but now they have been imposed a short delay (a week or two) to fix the problems, or they get a fine. The system seems to work pretty well.