I still have my 505 but recently bought a NC to get a little more capability. I love the SONY 505 layout and I have had it 3 1/2 years (since it came out). If I were shopping for a new e-ink reader I'd lay out the extra bucks for the Sony 950. I have become spoiled by the NC 7" screen and the 950 has the pearl screen for better contrast. Despite the press slobbering over Kindle, the Sony offers more open system options. I guess I'm a snob. The Sony just feels good in my hands; light, clear screen, excellent battery life and access to more market items without the need to convert.
Why did I buy the NC? I travel a lot and wanted a new reader that also provided a little extra (videos, photos, magazines) with a smaller screen and without the need to spend $700 for a proprietary baseline.