Why am I losing visits because of changed permalinks?

About a week ago, I had an issue with all my individual pages coming up as 404 errors right after I upgraded to 3.1, but the home page was fine. Someone on this support forum told me to change the permalinks from day and name to default. I did that and everything returned to normal, I guess. But now today I’ve noticed that I’m only getting a third of the visits I usually get, and this has been going on for the past three days I believe. Google analytics, StatPress Overview and WP-Stats are all showing roughly the same percentage decrease in visits over the past three days or so. I’ve still got the individual pages’ permalinks on default, but when I google my own posts and click on those links in google, it comes up as a 404 error. I’m losing a lot of visits because of this, and I would really like to be able to get my permalinks back to day and name, instead of default.

Any help in this matter would be appreciated.