With about half of Twitter users able to access Twitter Lists as they’re rolled out to everyone, independant Twitter list directory Listorious has been quick to launch and offer curated lists on a range of topics.

It’s interesting to see whether the relatively peer-led recommendation of Twitter lists will displace directories of individual users grouped by category such as WeFollow and Twellow. Obviously there are concerns about both the follower-inflation that everyone has seen from the Suggested User List presented to new users, as well as individuals worried about being pigeon-holed and lists becoming reciprocal favours rather than recommendations.

It’s also likely to diminish the value of the longstanding Twitter tradition of #followfriday.

From a business point of view it makes utter sense for Twitter to have some input/control of listing users – all the examples above have been relatively successful. What’s the betting that an option to promote a specific list could be in the monetisation plans? Spend some cash and your list could be promoted to everyone, or possibly replace the Suggested User List for a period of time?

Suddenly they’d have a route for grabbing sums like the $250,000 offered earlier this year by Jason Calacanis, without it being flagged up as obvious in a list of just 20 or so people.

And obviously list pages themselves offer individual sponsorship/promotional oppportunities…

As a user of Twitter, I’m undecided whether lists will be a positive thing on balance, but as a Twitter observer it’s one of the biggest steps they’ve made in a long time towards making money.