It's kind of hard for me to say what happens to people who finished outside of the top 30-50%, because (as wustl3l says), almost no one talks about grades or jobs, so I just don't know who had what grades. I certainly knew a number of people who didn't have jobs at graduation, but I'm not sure how broad or extensive their job searches were. From what I know, most of them now have jobs, though they had to do their own legwork (networking, etc.) to get them. My sense is that the people who have the most trouble are those with mediocre-to-bad grades who want to work in locations that tend to attract people from schools ranked above Wash U.
As for CSO, it worked well for me (I got a summer associateship through on-campus interviewing). But I know a lot of people complained about it, probably people whose grades weren't so good. I hope it's improving.