Twitter has dropped a message onto its status blog to say that it's testing a new set of notifications for those who use Twitter.com to interact with the service. If you see a yellow bar at the top of your Twitter stream on the site, then don't be alarmed.
It'll say something like "3 new tweets", and clicking the bar will expand the page to show those tweets. Similar functionality has appeared in Twitter's search results for some time. The idea behind the move is to keep people staring at the Twitter site, "maximising engagement" as some marketer would probably put it.
The feature is being rolled out slowly, initially to a "limited" set of users. Twitter says that it "hopes to roll it out to everyone as soon as we can". For many hardcore Twitter users the feature won't be that useful - it'll rise too fast - but for more casual fans, who follow fewer people, this could prove a handy tool.