never make users do work that machines can easily do
Because they are manual and require people to do work. People hate to do work, especially when it’s upfront work for some possible future benefit.
To use a not too far off example: consider the success of Mint. A big part of it was that it automatically categorized transactions for you. It’s not perfect by any means, but it’s good enough. If they left categorizing up to the user, I don’t think it would have been as successful.
Exactly why the conversationlist idea occurred to me as soon as I saw Twitter lists in action: find ways for machines to take over the care and feeding.
It really surprised me that people who stopped updating their blogrolls after a couple of months didn’t see a bump in the road looming for Twitter list usage.