I have wrote about privacy before, and I really have to write again. Right after "vappu" (first of May), when veryone celebrates they have a job and get drunk (including me), there was news in Finland about mobile Internet browsing. According to newspaper Keskisuomalainen (article in Finnish) there are companies who have developed systems by WAP technology, which can track down and save mobile phone numbers of people visiting websites. By knowing someone's mobile phone number, you can also find out owner's name, address, gender and even occupation.
Would you, as a marketer, use this information for better direct marketing? I could recommend one thing: think twice! From technical point of view this could be quite easy and possible. Why not, I believe it. But, in analytics business, we should think and care about privacy. Although there's not a clear privacy law (yet!), at least not in Finland, this kind of utilization is offending visitor's privacy. As a consultant I can not recommend this to any company at the moment. If you want to do something like this, you should get visitor's permission for tracking beforehand.
In business to business marketing, which is much more relaxed about legal stuff than business to consumers, I do suggest to follow visiting organizations for creating a lead list for your sales team. But, in this case too, you should have appropriate terms of usage in place. Maybe a small link somewhere in the bottom of the page in your website... : ) Anyway, I think it's just a matter of time when there will be a clear law which will prevent some of the exploitations of innocent visitors.