Legislation in the House of Representatives would require Internet service providers to store subscriber data specified by Attorney General Alberto R. Gonzales. The Attorney General would also get to decide how long the data would be stored. The bill, H.R. 837, provides:

SEC. 6. RECORD RETENTION REQUIREMENTS FOR INTERNET SERVICE PROVIDERS.
(a) Regulations- Not later than 90 days after the date of the enactment of this section, the Attorney General shall issue regulations governing the retention of records by Internet Service Providers. Such regulations shall, at a minimum, require retention of records, such as the name and address of the subscriber or registered user to whom an Internet Protocol address, user identification or telephone number was assigned, in order to permit compliance with court orders that may require production of such information.
(b) Failure To Comply- Whoever knowingly fails to retain any record required under this section shall be fined under title 18, United States Code, and imprisoned for not more than one year, or both.

Giving law enforcement the tools to protect our children and put creeps behind bars obviously sounds appealing. And I gather it polls very well in Republican suburbs, too. But as I have pointed out here, the real problem is inadequate prison terms for child molesters and the fact that, once released, child molesters have been allowed to evade registration and notification requirements. Data retention is an attempt to outsource the enforcement and supervision burden.
But it may not be as simple as some people hope. Criminals are learning that they can access municipal and private Wi-Fi networks anonymously, according to a report in the Washington Post:

With nearly 46,000 public access points across the country — many of them free — hundreds of thousands of computer users are logging on every day to wireless networks at cafes, hotels, airports and even while sitting on park benches. And although the majority of those people are simply checking their e-mail and surfing the Web, authorities said an increasing number of criminals are taking advantage of the anonymity offered by the wireless signals to commit a raft of serious crimes — from identity theft to the sexual solicitation of children.
“We’re not sure yet how to combat that,” said Kevin R. West, a federal agent who oversees the computer crimes unit in North Carolina’s State Bureau of Investigation. “Free wireless spots are everywhere, and it makes it easy for people . . . to sit there and do their nefarious acts. The fear is that if we talk about it, people will learn about it and say, ‘I can go to a parking lot, and no one will catch me.’ But we need to talk about it so that we can figure out how to solve it.”
The way it works is simple: Anyone who has a wireless card installed in his or her computer — and most new computers are equipped with one — can access the Internet from any of the public WiFi “hotspots,” as they’re known. In an age of portability and instant gratification, getting online has never been easier — for law-abiding folks and those with bad intentions.
And in especially dense areas such as the Washington region, some neighborhoods might offer users a dozen or more open wireless signals from which to choose.

The article, by Jamie Stockwell, which is here, includes the humorous anecdote of an elderly woman who innocently maintained one such network and had to answer for it.
So, in order for data retention to work, networks will have to be secure. Even the one in your home. There will have to be a law, you know.
Cities will have to modify their networks, as well, to record who accesses them and which web sites subscribers visit. One way would be to require pre-registration and access codes. Cities will incur administrative costs, but since they will know who their subscribers are, it would be easy to pass these costs along to the people who use the service (and who thought they were getting it for free).
Data retention seems extraordinarly unwise when you consider that it could impose significant costs on consumers, create opportunities for hackers and other criminals that we can’t even imagine, magnify the devastation that trial attorneys and divorce lawyers can cause, not to mention the possibility for misuse by officials.