I think that this figure would be a lot lower than people expect. Normally in a web survey you would see Tuple (multiple extension) registrations where a company is protecting its brand. These Tuple domains tend to be on the same nameservers and often the websites are directed to the primary brand website.
As part of my work, I do domain stats every month for approximately 1.2 million active hosters and indepth reports for Irish webhosters. The domains on roughly 1K Irish hosters across ie ccTLD, com, net, org, biz, info, mobi, asia, eu, co.uk and .de extensions are analysed in detail for SOA, MX and WWW. The key extensions for Ireland are .ie (the Irish ccTLD) and .com. Outside of these extensions, the usage tends to fall away. The pattern with the Tuple registrations is that a company might register its domain in ie/com/net etc but might only have the .ie and .com versions active. The other ones may not even be set up. However the .ie extension is also more expensive than the gTLD ones (approximately five times). This does create a bit of an incentive to use it. The active/unique figure for .ie was over 30%. The level of parking in .ie is in single digit percentages. 01/June/2009 The breakdown for domains on Irish hosters also puts .com and others into a more realistic perspective:
EU: 7448 (72% coverage)
The number of registered .ie domains on 01/June/2009 was 125,840. However some of those are hosted on non-Irish hosters.
The mistake people often make with extensions like .com is in considering it as a single market. While over 80 million domains sounds impressive, breaking it down over ccTLDs can show a different picture. The suprising aspect is how important the ccTLDs of adjacent markets are in a country's domain market. The second most important ccTLD for Ireland is not .eu but rather .uk ccTLD.
Domain parking and PPC has, to some extent, interfered with the evolutionary process of domains and affected the domain environment for the worse in that it reduces the incentive to develop while increasing the Buy To Park demand. While the number of domains will have grown, the number of actively developed websites may not have grown at the same rate. The .com and to a lesser extent are mature extensions that are kept alive by the volume of their registrations. In net growth terms, they are close to being overtaken by the ccTLDs each month.