It seems that there are many different things people aim at when organizing their contacts in Twitter most notably (1) facilitating search, (2) reducing noise and (3) gaining publicity.

What do you think are other possible aims?

I decided to categorize by regions and organize into public lists.

Here is my blogpost on this: http://ibuchem.wordpress.com/2009/10/30/twitter-listen-einsatz/

I think it would be good to receive an email when you are listed to have the possibility to opt out / block a person as you also receive an email when somebody starts following your tweets.

The entire approval thing is not implemented in Twitter as danah boyd writes in her recent post on Twitter and Facebook status updates. You don’t have to follow back in order to receive updates on Twitter whereas you need to approve friendship requests on Facebook to have access to the other person’s stream.

I rather like that I am not required by default to follow another Twitter user but can decide on a case to case basis still allowing him / her to receive my updates in their stream.

The feature of being able to subscribe to a list of somebody else is good when I share their opinion about the categorization. If I really wanted to drill down I can still follow individuals or put them into a list of my own. The lists can be great to discover people whom to follow. That’s the case for any categorization / directory etc.: A pre-selection already narrows the field of potential suspects.

It’s interesting that I can put people in lists without having to follow them. Then I could have strong ties (people I follow) and weak ties (people who I only have in lists).

Having lists in the web interface is not streamlined yet because I have to go to each group to see the updates. Or did I miss anything? Client apps will be better once they have implemented the “official” lists.

Interesting subject of research will raise up

I am sharing your couriousity but: Each list has its own followers – this could be a good anchor to hook on a topic.

It has been possible to do this in an ad hoc way before (eg Tweetdeck group, or bookmarking twitter IDs to delicious and then using a Yahoo pipe to aggregate feeds of people tagged the same way), but the ‘true service’ offering makes this capability available to everyone without any serious barrier to entry.

The lists are also social objects that can be easily shared, as well as trivially subscribed to/unsubscribed from (though I’m not sure what happens if you follow a list that also contains someon you’ve blocked? Are their tweets blocked in the stream?)

I imagine the next step (eg in client evolution at least) will be the ability to filter tweets from a particular group so that you only see tweets within a group that contain (or mayb, do not contain) a particular term.

For myself, I’m going to explore the use of lists a hashtag discovery mechanism:
http://ouseful.wordpress.com/2009/11/02/whats-happening-now-hashtags-on-twitter-lists/