But to me search is about 'I know what I'm looking for so I ask for something specific', usually looking for a fairly certain answer. If this involves my search history, or people that I know, I will be able to tell the search platform that when I search, I don't want them to assume this on my behalf - this just makes my results less specific than I originally intended.
We (the HN community) are not the target audience for these optimizations. Ever watched your mom type in a search query? It's aweful, sometimes I'm amazed at the results Google can produce for crappy search queries. It's those people that will benefit tremendously from these kind of optimizations.
For us, who do not want the personalised search results, the standard answer has been that we should simply log off and it will be generic. While I do feel that Google should simply make this an account preference (so I don't have to log off from my gmail account just to be able to use search in a fashion I appreciate), I can clearly see and appreciate why Google is going for personalised search.
I think we probably use this feature far more than any other segment - terms we use for our technologies are often overloaded. I don't want to have to constantly specify whether I want gems to be gem stones or ruby packages.