In many other areas, Adelphia uses the dual-path asymmetric system (which requires a cable connection and a telephone modem connection). Some things about that system are different to what I describe here, and some are the same.
Firstly, a cable modem doesn't operate as a modem does, in that once you're plugged into it, you don't have to the connect/"dial" to a place that supports them. Adelphia does all that for you. So, once you're plugged in and configured, YOU'RE ON THE INTERNET! You have an IP address, and can connect to anywhere else, immediately and directly, just as you would from an office or lab on campus.
So this means that the place that you want to connect to does not have to do anything at all to allow cable modems to work with them. You just connect with telnet/ssh/rlogin/POP/IMAP as your would from any other host on the net.
It currently only supports dynamic IP addresses, using DHCP. They'll give you either Mac or Windows 3.1 or Windows 95 software to work with it. The service does work with Linux (or any other PC-Unix such as BSDI, FreeBSD etc., or even a workstation), but you're on your own with getting a DHCP client, etc..
My machine at home dual boots Win95 and Linux. And I have it working just fine with both. The Linux DHCP client daemon works just great. (The primary site for the Linux DHCP client daemon is in Japan, but the above link is to a mirror in the US.) Here is a cool Linux DHCP setup site. Update: The Linux 2.2.x kernels required a newer/different version of DHCP.
One thing that I must stress here: there is apparently a common misconception that because it is using "dynamic" IP addresses, that your IP address will regularly change out from under you. While this is possible, it almost never happens. Adelphia has DCHP configured to do 90-minute renewable leases on the IP addresses, and the DHCP system will renew the same IP address for you if at all possible. So, except under exceptional circumstances (such as when Adelphia switched from 207.24.69.* to 24.48.33.* in mid June 1997; and when they reworked it again in December 1998), once your computer is up, it will maintain the same IP address until you reboot it.
(Adelphia's tech support claims that they will eventually be supporting static IP addresses, but at an additional cost. And that the marketing and legal people are still working on the details of that.)
The service is currently available only in some parts of Amherst. You'll have to call Adelphia to find out when it'll be available in your neighborhood: I believe that most of Amherst/Williamsville is now covered.
About the speed: it's 10Mbps (that mega BITS per second) from your computer to the cable modem. And that is symmetric - 10Mbps in both directions, both over the cable. It works with any 10baseT ethernet card: the cable modem plugs into the cable on the one side, and gives you a regular twisted-pair cable on the other side.
I don't know the details of the network topology within Adelphia's system; other than the world is split up into nodes/neighborhoods, with all the subscribers in the same neighborhood sharing the same conceptual 10Mbps at their "head-end". I presume that their nodes are connected to each other by something faster than that.
From what I understand, their network connected with a (partial?) T3 (about 40Mbps) to the Internet.
They do provide a proxy web server, so, for web surfing, if you configure your web browser to use their proxy, and you go to "common" websites, you can get full 10Mbps speed between your system and their web proxy. And, similarly, for reading news, if you use their news server, you also will get full speed.
They also give you all the regular ISP services, such as mail hosting etc.. They claim that they will be providing dial-up access too, at some point, so that you can check your @adelphia.net mail when away from home.
The regular cost is: (when I had it installed, in 1997)
My understanding is that their rationale of $40/month is: a second phone line usually costs about $20 per month; and an ISP with unlimited access usually also costs about $20 per month. Hence their $40/month cost - about the same, but with much greater speed than you can get through an ISP and a phone line. Of course, for us at UB, who don't have to pay that ISP cost, it is more expensive.
Overall, I'm happy with the service.
In other words, a T1 is plenty fast for most average stuff that one is doing. But it is indeed the limiting factor is large uploads/downloads/transfers between campus and the Adelphia system.
However, in some other Buffalo suburbs, and in some Pennsylvania suburbs, that Adelphia is using, and/or is planning on using, the uni-directional coax, and requiring a telephone line to be used for data transfer from the user back to the Adelphia system.
There is a contract, with lots of details. Mostly covering themselves, in terms of them not being responsible for what you do, nor for what you happen to get from the net, and also the "no-warranty" type stuff. Also, you're not allowed to sell service etc. to others (but I don't recall exactly what else that allow/disallow you to do in that respect).
No usage limitations: I believe that they're happy with you staying online 7x24. I vaguely recall reading something about them getting upset if you use excessive bandwidth, and that they might want to upgrade you to a more-expensive business connection if you do. But I don't recall the details.
As to time-period, there is no contract on that: it's simply a month-by-month thing; charged to your cable bill.