Looking closely what I see is Google, twitter and friendfeed have just a one point of interface between the user and application. What do you think is possible if we are if you are allowed only one input box for your idea.<p>* Google Search: One input field (Rank 1)<p>* Twitter: One text area (Rank 11)<p>* Friendfeed: one text area (Rank 735)
If you have more than one feature and only one field, you will inevitably end up with conventions for smuggling extra data into it, which users will then have to learn. E.g., Twitter has @user and #tag, and Google has site:, inurl:, and cache:.
Well, technically they all have other 'stuff' to help you do whatever it is with that single box. Google is the only one that doesn't require you to signup before using it. Digg and HN kind of only have 1 input box.<p>It definitely is an interesting trend. I've even tried to come up with startup ideas restricting myself to simple inputs like a single textbox. Sometimes adding some constraint helps you be more creative.
I would focus less on the input box and more on the task. Each app focuses on a single task presented with as few options as possible. it's hard to use any service wrong because there is not much to mess up as a user.
Try to make a calendar app with only one text field. There is no way "one text field only" can be applied as a general rule, but just thinking about how you could apply it will (IMO) make your app better.<p>What the apps listed above have done is simplified the interface to the <i>bare</i> minimum needed to accomplish the task. Sometimes, that requires 5 text fields, sometimes 1.<p>The biggest value of a good user experience designer is in figuring out the minimal functionality for each step in the application and stringing those together in ways that make sense.
Interesting...I originally had a more complicated interface on <a href="http://buyersvote.com/" rel="nofollow">http://buyersvote.com/</a> where people could add/remove items on a list which would pop out a new text field for each item.<p>I eventually just made it one big text area and let them do "one per line".<p>There is a still a sparate field for the title. I don't have any hard data on whether this change improved engagement or not. But I think as a general rule, the simpler you can make the UI the more engagement you'll get from first time users.
Questioning user interface dogma in your field can have interesting results. I'm building a DNS service at the moment and having experimented with a few user interfaces, have found the one I like the most has a single page for viewing and editing the zone, fixed record names and types, no class or TTL (at all), and a field for each unit in a records data, rather than the traditional one data field per record data. It's more limited than other interfaces but it's also more powerful; have to wait and see whether the market agrees.