Germany (and probably other countries n the EU as well) considers IP addresses PII, and you have to have consent to store it. Short-term logs might be justifiable as technical necessity (but the lawyers I've heard talk about it didn't want to put a "safe" time frame on that), but certainly not "keep as long as possible".
That's the reason Google Analytics, Piwik and others have an option to blank out parts of the IP address.
Jail is a bit dramatic though (at least here), unless you do something bad with them fines + maybe damages would be the maximum, and it is quite unlikely you'll actually get hit. But if you are ever in a situation where this would come to light (= already in legal trouble), it could make things a lot more complicated, especially if you process data for other companies.
It falls under personal data about someone. Many (but not all) EU countries consider IP addresses to be personal information, and hence "Store it forever for no real reason" is illegal. You need to have a legitimate, legal, reason to store PI, you need the person's unambiguos freely given consent, etc.
There is currently a court case as to whether dynamic IP addresses from ISPs counts as personal information. But static IP address probably count. And all the other information (user X logged in at time Y and send message to other user Z) would be PI too.
If it's true, you'd think it would be widely-known and publicized in those countries (whichever ones they are) but I can't find any reference to such a policy existing anywhere.