When it comes to UI, I do believe that an effective UI does not need any user guides or further explanation. Yes there might be product related terminologies which at times need a few accompanying words ( like a tool tip ) but if the feature is complex enough then there should be a different approach - wizards or quick visual tour while the user is performing a function.Also the concept of contextual UI gels with me.
Term Alert :
Contextual UX anticipates the user's next actions / purpose and renders the information before the user asks for it
There are small changes which are effective in the long run - e.g. if a logo of a merchant is added on a financial account statement, it makes the transaction easily recognizable.
However I have some polar views on UI when it comes to innovative products. Users are getting more and more tech savvy and easily learn new features with a little playing around as long as they are kept engaged and interested. There is a small window between curiosity and frustration and crossing the line would lead to potential loss of the customer. This is where content comes to the rescue. Majority of the UX designers are adept at considering all HCI elements and empathy maps further aid their understanding of expected customer behaviour. Add to it rapid prototyping, A/B testing and user acceptance testing and we have a fool proof process in place.
I dislike the term user testing - the user is certainly not being tested. Its the product which is under the scanner and the test is if the product will be accepted by the users or not. User Acceptance Testing aka UAT is a better term.
Lately I have been minutely observing even day to day interfaces - GPS in the car, the elevator panel, POS devices and am amazed at how small changes in them could have enhanced the user experience considerably.
I went through a few talks by Don Norman ( the guru of Design ) and he did provide insights into so many overlooked daily design flaws. Now when I go to a restaurant which has the traditional salt and pepper shakers I do remember his words 'it doesn't matter what you think - whether the shaker with less holes should contain salt or vice versa ; its dependent on what the person filling them thinks' - ah, some debates will never die !