See, that's the problem - the search form on the extend/plugins page here doesn't seem to do a boolean search - in fact, it doesn't seem to use your search terms at all any more. For the past day or so every search I have tried to do returns the same results, and that is very, very frustrating.
As for searching with Google, putting quotes around it will search for that string. You can also do things like:
site:wordpress.org/extend/plugins "improved plugin installation" -tags
Which will search for results that have the phrase "improved plugin installation" but does NOT have the word "tags" in it. It would be nice if the plugin search here could do that - but not sure if anyone has even looked at the problem yet. :(