`(h) Retention of Certain Records- A provider of an electronic communication service or remote computing service shall retain for a period of at least 18 months the temporarily assigned network addresses the service assigns to each account, unless that address is transmitted by radio communication (as defined in section 3 of the Communications Act of 1934).'.
That's it, that's all there is to it - DHCP assignment log preservation. My Comcast DHCP-assigned IP address did not change in over a year, chances are most people's addresses are not changing over the discussed 18-month period at all. The law changes nothing for most people.
For the government to know if you visited certain site they would still have to get the traffic logs from that site.