This only works for languages that provide dot-like syntax. E.g. in Python (which is a little bit inconsistent in this regard) the equivalent would be "len()" and I am not sure how it should work there, as there is no context to infer the function/method.
I get your point though and there are cases where completion might be useful, but for me the context-switch to a search engine is just not that much of a hassle, but maybe I never enjoyed a good completion engine, so I might give it a try.
Jedi (I use it with Emacs and auto-complete) does a fairly good job for Python. While the `len` being a function screws things up a little, there are many places where you can still use autocompletion the way I described, specifically:
import module
module.<TAB>
and:
def meth(self, ...):
self.<TAB>
and even:
foo = Foo()
foo.<TAB>
It doesn't work for all possible cases, but as you said, you can always consult Google. It's just that I prefer not to leave my editor if I don't really have to.
OTOH, I work with a lot (10+) of different languages and find even the dumb, basic autocompletion (which only offers to autocomplete words already present in the file) helpful. As other commenters noted, writing aLongAndDescriptiveFunctionNameToCall from memory every time may be inconvenient for two reasons: a) was it aLongAndDescriptive... or aDescriptiveAndLong...? and b) writing this much text takes time, and the more letters you have to type the more probable a typo gets.
Anyway, I think you should give a try to a few different auto-completion plugins/systems and see for yourself. You should probably spend a little time to configure such a plugin so that it doesn't get in your way when it fails (ie. has no good completion to offer), but once you make it so the auto-complete may become really helpful to you. Or it may not, but I think it's worth checking out.
or use ctrl+shift+space in intellij and it will just show completions that return type maching the left side of equation :) or press it 2 times and it will look for all aCollection.. for the matching types ;) very powerfull
Basically, (semantic) auto-complete is an inline quick-search facility for docs. Very, very useful if you know how to use it effectively.