[joshuahedlund]

Your initial takeaway might simply be "wow, a lot less people user Twitter than Facebook." However, I remember seeing stats a year or two ago suggesting that 50% of US users had Facebook and less than 10% had Twitter. If both sets of numbers are accurately comparable (and they may not be), that would suggest that Facebook may be on a slow decline while Twitter is still growing.

[diego]

I don't think old stats from other sources are comparable. In order to evaluate changes I would only compare my results against the exact same question asked with the same tool at a different point in time.

[sharkweek]

in my experience, Twitter, at least with many people in my social reach, is a lot more vibrant and interactive, despite less adoption as a whole. Facebook is great for the occasional photo dump, but I see the news feed slowly dwindling in activity, especially when compared to my very active Twitter feed