What do you want to be able to customize?
tsally: I know what I _don't_ want to be able to customize.  What I can and can't see.  Similar sites give the ability to block submissions or comments from a particular user.  I think this is a horrible idea given the special nature of this community.  The most defining aspect about Hacker News is its high quality.  Any type of ignore feature is just going to take away from that.  Just because you can't see the garbage doesn't mean it's not there.  The flag feature is already sufficient; ignore functionality would be a huge mistake.EDIT: I just had another thought.  I also believe that any type of functionality that allows the categorization or filtering of topics would be bad, for the reason outlined above.  If there are too many high quality stories that people need to filter or categorize them, the rate at which stories fall off the front page should be increased.  Having too many high quality stories is a fantastic problem, but it should be solved by being more selective, not by filtering.