The Canadian experience
From my view in Canada, as a professional pilot and a private aircraft owner, our privatized ATC system is a huge improvement from the days when it was government owned and run. Nav Canada has had the stable budget needed to make investments to improve the system.
The big fears when privatized ATC was first discussed in Canada were potential significant cost increases for private owners, and a potential incentive for private pilots to avoid flying IFR or getting weather briefings, if they were charged for those services.
These concerns were fully addressed when the system was set up. As a private aircraft owner, I pay about $CAD 77/year, tax included, or about $US 55. There are no extra charges for IFR, weather briefings, ATC services, etc, as long as I avoid less than 10 of the busiest airports in the country. Considering the amount I pay annually to fly, $US 55/year is a drop in the bucket.