The same as driving licences, TV licences and all of the other governmental ripoffs that plague our existence. The user pays a yearly sum for the licencing costs (plus skimming, payoffs and monopoly abuse as per standard practice) and receives an official card or certificate.
For enforcement, perhaps ISPs could be required to ask for certification before supplying a connection to a household (If there is a certificate holder in the house, he/she would be responsible for the behaviour of those in the house). I suppose it would have the enforcibility level of a driving license. Spot checks, maybe?
Right. Governments are already spending too much in too many areas. Having them, and we know how technically advanced the government is, license this is hugely impractical. And ISPs are in the business to make money. Who's going to pay them to do the "enforcement"? This would be challenged heavily in courts since ISPs are not trained for enforcement (it'll raise ISP costs if they have to be trained under guidelines similar to police officers and other law officials).

And then the possibility of forged certificates?? What about people pretending to offer courses so you can get your "license"? Or pretending to act on behalf of the gov't to issue the license? Would it be specific for Microsoft only? So if people used Linux/MacOS, they wouldn't need a license (don't get spyware and/or worms to the extend that MS products do)? What about foreign countries? Are we going to force them to follow suit? How do you convince them to be part of this when their budgets in many cases just can't handle "one more thing"? There are quite a few people online from the UK, Europe, Australia, China, India.

You pan ads because of a lack of ROI. And you think this is going to create an ROI!?

A certification system would have potential income for the authority, with admin charges and fines... assuming the authorities would front the initial setup charges.
You've never seen a gov't implement a simplistic certification program have you? They tried to implement a gun registry here in Canada (it's running). It was supposed to cost something in the $2 million (IIRC) and eventually pay for itself. At present, it's well over $2 BILLION. I have little to no faith in having the gov't run this. In addition, particularly for those in the US, what additionally layer of Big Brother would this add?

Interesting but I don't think it's a pratical idea.