KC Lemson writes a nice little bit about how hard it can be to design a feature and get it right. She writes about the type-ahead feature in the Outlook Web Access listview- this was the most visible thing they added in Exchange 2000sp2 and was a huge improvement. Of course the amusing thing about her write-up is that while a bunch of folks were stressing about all the different permutations of how to do things, a dev (I'd have to guess it was Jim but I could be wrong) just coded it up and you could feel right away that it worked great. In some ways this anecdote is almost a counter-example to her main point (and Eric Lippert's where which is where I got the link). It turns out that if you took a different approach to the problem (just prototype it, go from there) sometimes the solution can be pretty obvious.

Which isn't to say that sometimes you don't have to do things the hard way. Even with the quick-just-prototype-it approach, usability testing is vital (I'm actually sitting in a usability test right now) and for some things (core OS stuff like Eric's VBScript/JavaScript engine) pretty much everything needs to be done the hard way.