How does this differ from Programmers? Nothing in the site description looks like it wouldn't fit there or on Stack Overflow.
Programmers seems to be more about the role and position of programmers, rather than about discussions on design per-se.
As for SO, the focus seems to be on solving specific "how to problems" or debugging questions, with various languages and frameworks, such as "How do I connect a signal to a slot in QT?"; "I have this code -I want it to do X, but it doesn't - what's wrong with my code?", etc. Design and good practice seems to not to be the focus there, although sometimes they come tangentially into the discussion. I generally don't have too many "how to" questions, but I have lots of design and best practice questions. I sometimes post design oriented questions on SO that don't really get much attention.
Software Design - how to write GOOD code and design robust systems - is a separate discipline completely from the dirty details of everyday implementation. Some very important books have been dedicated to this area of development, such as "Code Complete" and the Gang of Four's "Design Patterns". It generally interests more advanced, senior level programmers who know how to do the every day tasks and have moved beyond that - it's about the "Big Picture"