The "social search" experience with Google+ has been underwhelming so far, to say the least. The problem is largely one of relevancy: Most of the Google+ stuff that gets dragged into my searches is completely useless and not relevant to the search at hand. (I would guess because Google's trying to make something meaningful out of often loose connections between me and other people.)
My Gmail, on the other hand, is a world of almost nothing but relevancy. It contains basically all the things I talk about every day — with the people most important to me — stretching back for the last several years. Along with crucial data, like flight numbers and doctor's appointments and restaurants I might go to next week. If Google can't make relevant search results out of that — the very fabric of my conversations — it should probably get out of the social search game entirely.
Having Google Search trawl through Gmail might creep some people out, but since Google changed its privacy policy and started looking at you as a single user across all its services, turning on Gmail search won't fundamentally change the relationship between Google and your data. (It won't be be any creepier, in other words.) Google already serves ads in Gmail based on the content of your emails, anyway, as Microsoft is fond of pointing out. So go ahead and sign up for the limited trial — it'll roll out to everybody eventually anyway, and you might as well get better search sooner, not later.
Oh, two other things have changed in search — again, for the better. It's like good ol' Google. Search is also now listier:
And Siri-er on the iPhone:
