This has been annoying me since I started using wordpress. The searchfunction for plugins is in fact useless. There is no way to filter your search. Let's say I want to search for a widget plugin that lists Tweets from my Twitter account. If I search for Twitter, a lot of plugins pop-up, but a lot of the plugins do not have widgets, forcing me to manually go through the entire search result by hand to find what I am looking for. Also, if I want to sort my results after update date, rating or whatever, there is no such function.
In the end, the search is extremely tedious, and I always end up Googling for hours to find the right plugin. And when I find it, it is usually outdated.
Please, create an advanced search function for plugins with filters and sorting. And while you are at it, do the same thing for themes.