flowersmoker

I googled this for a bit, and while Google did not do a study on opening links in new tabs/windows, it seems like the University of Washington and Microsoft did: http://jeffhuang.com/Final_ParallelBrowsing_HT10.pdf

Just skimmed the abstract, which says "We find that users switch tabs at least 57.4% of the time." but looking at Table 1, it seems like 64% of people do not open search results in new tabs/windows at all, so your initial guess is about correct.