I will take a .nets for keywords, cities or generics. For end users that can't get the .com it is often "the second best option". What really matters in the end is the content, website design, SEO, links and advertising...basically having the "website product" that will make a site successful for an enduser and not only get traffic but REPEAT visitors and referrals. I believe one of the key search engines algorithms looks for keywords and relevance to the search. In that instance "bulldozer.com" and bulldozer.net" have a fairly level playing field for those searching that term. The big value can be for the enduser that buys the .com and will pay whatever to obtain the .net too!
In terms of percentage of registration, I think that in ascii .coms register 10 to 1 to dot nets. In idns, I believe it is currently running 3 to 1, but the percentage of .nets will probably drop as registrations increase.