The Stack Exchange Network contains [a lot of sites](http://stackexchange.com/sites) and it works especially well -- particularly when used in combination with a search engine -- for answering one-off technical questions.  But what is Stack Exchange _not_ good for?  

For instance, it doesn't seem to provide "paths" through existing questions and answers that people could use to learn a subject from scratch, although this might be a good idea!  It doesn't seem to want to be an encyclopedia (or does it?).  

Indeed, it seems to "do one thing and do it well", which is of course a great model for success on the internet!  Are there plans to expand the interaction model, or are the limitations seen as good and healthy ones?