Twitter 'Lists' are now live for all users.
"We’ve been taking our time rolling out the lists feature to make sure things go smoothly and developers have a chance to begin experimenting with our Lists API. For example, TLISTS will provide tools to efficiently build, measure and distribute Lists, while Listorious hosts a directory of 'awesome lists' on Twitter.
Anyone can curate and publish lists, so if you have an idea for one, just click "New list" in the sidebar of your Twitter account and you're on your way. Add accounts to a list using the "Lists" drop drown on a profile page. We believe Lists will be a new discovery mechanism for great tweets and accounts."