I have a CS degree from a major university. I have to disagree with most of the comments I've seen so far. Things like design patterns, proper object modeling, even advanced data structures and algorithms can be picked up on your own with a bit of effort as you need them, and experience building real production used software is the key to hone those skills.
IMHO there are two things that I got from school. How to properly analyze code (in terms of processing time, memory usage, ...) so that I could accurately predict how it would behave under different conditions (especially when some of those conditions can't easily be tested). And an introduction to a large swath of computer science terms and facets, so that years later something comes up and I have a faint understanding of where to start looking.
The code quality, design, and ability to apply [insert new hot term of the day] correctly all come from real world experience. And I do think you have to get that experience in a professional setting (I would consider much of the open source world profession, just FYI), hobbyist work just won't let you grow the way you need to.