There's little incentive in filling out a form that disappears into the ether. Given that Google's other web-based support tools are mostly useless and unanswered (Gmail support for example), this is not much an incentive to waste time filling out another form and likely getting no reply whatsoever.
I know that the search quality team loves getting specific examples of bad search results. I know this both from talking to them and from seeing how they interact with people on forums (HN in particular :-) )
I don't work on search quality, but I can pretty much guarantee that if you send specific examples to the search quality team, either through the feedback form, or some other means - heck send it to Matt Cutts - it will be looked at and used to improve search quality.
The more specific you can be, the better.
"Searches for bikes suck for me" isn't very useful :-)
"When I enter the query 'blah blah blah', the following urls (url1, url2, url3, ...) are completely irrelevant to me." Even better, say why you think the urls are irrelevant.
If you submit reports like this, I can promise you that the search quality team will take them seriously and will praise your name (if possibly only internally :-) )
