Jeff launched this thing by tuning it for what he wanted in a Q & A site. Since he is exactly the sort of early adopter they needed for the first one (for programmers) that worked OK. But now they are launching a fully baked, "Jeff-tuned" product to other populations and I think there will be problems. The problem with an overloaded page is that you've closed off your options - you've made it really hard to iterate. Because every piece of available space is filled with information it's very difficult to test the product with new users.
This happened partly because this is every programmer's instinct, and partly through Jeff's misunderstanding of Edward Tufte's concept of "information density". Somewhere in a Stack Overflow podcast Joel is telling Jeff that there is way too much stuff on the page and Jeff defends that as being an example of information density that Tufte would like. Not true - a vector field has information density: http://www.google.com/images?q=vector%20field When you can apply a single (simple?) rule to understand a lot of data, that's information density. By contrast, Stack Overflow is like any web page in that each element must be examined in turn to be understood. That's why you must eliminate elements ruthlessly, especially when you are starting out.