To clarify, the UN wouldn't be controlling things like popup ads. The plan was/is to investigate turning ICANN functions over to the UN.
Basically, this means the UN would run top-level DNS servers (hostname to ip translation) and netblock assignment. Only the former really affects most people significantly. More than likely the UN would run both with roughly the same policies that guide ICANN now, only they might increase fees to turn the internet into a revenue generating machine.
There'd probably be a bit of revolt on principle, but the likely consequences are price increases for domain registration. You'd still get spam and popups, and the UN wouldn't protect you from viruses either.