Today I've been surprised to see different posts when logged in - specifically, in the corporate video forum, a whole thread disappears if I view logged in today compared to not logged in. If I disable third party cookies on your site (using webdeveloper in FF) the issue goes away - all the posts appear to become viewable again.
I have the same view options (View:New Today and View posts by Thread) selected, so it seems to be a third party cookie affecting post visibility ... strange.
There is no issue, it is because I have worked with the team to develop a filter that allows us to feed posts to users of relatively-like levels of experience, etc.
This way, the many lazy people that will not use the search engine and ask the same question that was just asked three posts down from what they just posted, will not show to the more experienced users -- instead, they will show to the users from the middle to the lower level of experience. Thus, keeping our more experienced users from being buried in the same questions over and over.
Considering that we get 2 million users a month, it leaves at least a million users a month who are "qualified" to answer any question in the COW and questions are still being answered.
Consider it a pat on the back: our mechanism has assessed your "score" and determined that you are more experienced and so it is keeping you from some of the newer user traffic.
If you do not like it, you can go into your account settings and there is a control that allows you to see newbie/all posts. By default we are filtering, you can override it.