My answer is I don't know but I think it should
Most people would agree that well constructed things are better than shoddy things. I wouldn't buy or trust anything if it had a label on it saying 'This item contains basic errors, use at your own risk'.
To quote
WDG;
'When you buy a household electrical appliance, you can choose from a range of options. You don't need to ask "does the power supply in my house support Hoover or Electrolux"; you know it supports both, and you are free to choose. That's because there is a standard for mains power, that is observed by everyone concerned - the manufacturers, the power supplier, and the electrician who wired your house.
Exactly the same argument applies to the Web, unless someone subverts it. The difference is that fewer end-users have the confidence to make a fuss when they've been sold a dud. Valid markup is one of the standards that make it work.'
If I employed an electrician to fit some new sockets and on completion s/he informed me that they didn't conform to the appropriate standards but they work, I would understandably be very concerned. Why should it be any different for web designers?
It's about Attitude
A designer/coder who takes care to make their site accessible and user/browser/platform-friendly also has their clients' interests at heart. By being aware and professional, the designer can maximise the credible audience by creating valid code. Most of the errors I come across when reviewing sites are sloppy, thoughtless things like missing ALT tags and table SUMMARIES. As a result of laziness or ignorance, the shoddy designer alienates people using screen readers.
Similarly, designers who focus purely on getting it right in the error-forgiving IE may well alienate the tens of millions of people using Firefox, Opera, Netscape and Safari etc. who may well be pointed (by a search engine) to a dogs dinner of a site.
I realise that there are picky little bits of non-validation like & instead of & in link strings but most warnings and errors spotted by W3C and other validators are important and need fixing.
You Asked the Wrong Question!
'..do you think it matters about code quality and ranking?'
I know I keep banging on about this but websites are for human beings. Designers are too often fixated by their sites' performance in the search engines, constantly trying to get one over the opposition, exercising the latest theory about the current Google algorithm. All well and good to a point but actually what your human visitors are looking for is the same as the human created bots are looking for...quality content. Chances are that if your website has good informative content, is accessible to all, is standards compliant and reassures it's audience that you are credible, the site will also do well in the search engines provided that a sufficient number of other sites agree and link to yours.
Your human visitors should always come first and that means creating valid, error free, cross-browser proof pages. Once you've got that right you can focus on the nitty-gritty of
SEO. If you get to the point where you have to ask whether your errors are important to robots you have failed the first task.
I'm dismayed by bhartzer's comment that 'It doesn't really matter much at all', if he's correct. To my mind it would be fair and reasonable if all of the SEs rallied around the compliance issue and gave extra preference to sites that validated. Otherwise they are implicitly condoning exclusivity and sub-standard craftsmanship.