This new feature has to be enabled by the Twitter user in the settings page. Otherwise, there will be no changes and things will remain status quo. Twitter will use an algorithm to determine which tweets are more important to each individual subscriber. While testing the new feature, it was discovered that those using the new timeline were more likely to use Twitter more by sending out new tweets and retweeting older ones.
The changes will be launched in the "coming weeks," but not before Twitter gets some feedback first. You can test this new timeline out by going into the settings of your Twitter account and selecting 'Show me the best Tweets first.' Comments and feedback can be sent to Twitter at this link.
source: Twitter via Crackberry