being able to change your IP addy don't matter really (cept for maybe hiding from a hacker) cause there are still records associated with said addy as it pertains to a certain time frame...i.e. @ 1:15am on blah, blah, blah, a certain specific person was using a given addy....

one poster has also made an excellent point in regards to modems...they are all unique, and all are ID'd via tags that are specific to that individual modem (and also routers, and also NIC cards), so even without a specific time date stamp, a user can be ID'd via their mac address (id tag for above items) over a wide time period (like the whole time they were in posession of said piece of hardware), knowledge of said mac address also gives certain ppl the ability to track your actions all over the net....

so, in a nutshell, of course your dynamic IP addy can be traced directly to you, and only to you given the fact a person has a time/date stamp to place you as the 'owner' of said IP addy at a specific time