With respect to the specific question on what is an IP address, in some ways it's our location on the Internet. That same IP address can disclose—and I commend the Privacy Commissioner's report on this—more than just the computer or the device we happen to be using, because that information gets placed in many places all around the Internet. For example, if you're involved in a Wikipedia edit, your IP address is logged and becomes publicly available. There is the ability to use even that kind of information to begin to develop a profile of someone's activity online.
You highlighted it, but I think it's worth emphasizing that under PIPEDA the exception for law enforcement as currently structured today is by no means limited to basic subscriber information. This notion gets propagated again and again, and I'm sorry but it's simply false. The opening is to allow for disclosure, full stop. In fact at this committee you heard from the RCMP that it includes transmission and tracking data, but frankly, it could in theory include content as well from an intermediary who has it, if it's part of a lawful investigation.