Concerns about this seem overblown to me. I get regular comparisons as I have a tablet device that's not linked to any account and also use more than one search engine or browser. I find a marked improvement in the quality of results when I'm logged in, particularly when I'm researching legal or academic topics where I'm more interested in primary sources and long-form article coverage than in (more popular) blog and mainstream news outlet coverage. The other benefit is the personal blocklist, which automatically filters away a vast range of stuff which I know to be crap.
