For Reddit to save itself, it needs to put a major effort into the 'recommended page'. Iff the recommended page delivered a tailored experience to each user, then it would not matter (nearly so much) how many 'Digg refugees' arrived on the site. If your interest is programming, your recommended page would show you a programming site with articles that interested you.

The social media site that gets this right will solve the issue of the constant migration of thought leaders - slashdot - Digg - Reddit - ?Y Combinator? -?? If the recommended page really worked, it would become the user's default page, and thought leaders wouldn't have noticed a change in demographic.

Someone will turn these nomads into sticky participants, and then they've constructed a durable competitive advantage.

(edit typo)