http://dev.dota2.com/showthread.php?...=1#post1086255
http://dev.dota2.com/showthread.php?...30#post1082330
obviously this doesn't mean you're unable to queue into some people, just less likely. you also get additionally put in low priority should you get enough reports.
i played a few soloqueue games on a friends account last week. every single one of those games were terrible experiences. everyone was pinging, some dude was screaming into his microphone. there's less than 200 rating difference between our accounts. first time i saw people fight over mid in i don't even know how long.
i know it's anecdotal and i know the dev isn't specifically saying they do it for flaming or whatever, but i really do believe this to be true.