The only way an IP address can be traced to an individual account holder is by going to the ISP with a court order to get their records. And note that even doing this will not determine for certain whether the account holder was actually the one using that IP address. By itself, an IP address is useless for identifying individual people.

That isn’t entirely true. In cases where there is a static IP leased via an internet service provider, the name of the user of that address is entered into the Whois information, even if there is no domain name registered. I found this out the hard way a while back when I had a static IP address for ADSL service via my local telco. Doing a reverse lookup on the IP address assigned to me gave all of my contact info (including name, address and telephone #). Needless to say, I wasn’t particularly happy about this, but was told that it was standard procedure.

Laws may have changed since then, which I hope is truly the case especially when ipv6 gets a full rollout, because all of those addresses are going to be statically allocated.