We are creating a web application with a Twitter-style list of items, with a new item being added/shown once every few minutes.
A subject for debate is whether we should show new items automatically as they arrive, or display an incrementing total in a banner like "x new items".
I think the former approach needs some visual style added to new items, perhaps with a way of removing styling once they are "viewed" (how that is defined is a separate issue). The question were stuck on is, is there any accepted standard for this sort of UI or would it be a 50/50 choice entirely reliant on testing with our users?
A thought: We're wondering whether the amount of time people spend reading each item vs how often items appear is a factor. If people spend longer reading an item than the time between new items, then a "X new" would result in less interruption (UI changing as they read).