Google has been manipulating their algorithm, with the goal of making it more friendly to users.
This means it will find results that do not match all of your criteria, but are more "meaningful" ~= higher page rank.
They have also ditched the + operator (+keyword) which forces only results that contain matches for that keyword. They have added a verbatim option hidden in the left rail (you have to fold out to reveal it) which should make it so all terms must match. Also wrapping a term in quotes should also force things.
In the end results get more fuzzy, and when you know exactly what you want, it just pisses you off.
For example, I am trying to find javascript code for calculating TrueSkill (it is an algorithm that XBox uses that is used for their ranking).
So I type in +"TrueSkill" +"Javascript" and do a verbatim search, just to be through (because every other variation still didn't get me what I want.
What do I get, some results with Javascript in it, some with TrueSkill in it, and a one with both.
I go over to duckduckgo: http://duckduckgo.com/?q=%2Btrueskill+%2Bjavascript
And what do we get... success. Only the results that I want. Each only contain both results.
ddg is now my bitch when it comes to finding some specific chunk of code in a sea of unrelated crap.
Bonus points for having a search url which is not ridiculous.