Mockups, save you time (see: money) and unquestionably help establish expectations on what an application will generically offer and what the general layout will be. 
I believe I have found the tool that does this as quickly as humanly possible: Balsamiq.

There is not much to say about this topic so I'll give you the 15 second sell.
1. Fast
2. Generic enough so the business owner doesn't get caught up on aesthetics but understands exactly how the user will accomplish their task
3. Very easy to use. The first time I used this product I was cranking out mockups in minutes! Think about that.

--This isn't like Visio, (caveat: I have my own personal demons with Visio), but in short, you won't be making mock-ups in minutes. Sure Visio is good for architectural stuff, but the insight architectural diagrams offer are generally high level and I would argue, quite fiercely, pen, paper, and cell phone camera, would be a better/faster/cool in a hip start-up kind of way, solution to Visio...I digress...but seriously Visio is terrible.

4. Balsamiq supports many different types of mock ups: mobile, web, core platform applications (Windows and Mac)
5. Export to PDF
6. FAST. Did I say this already? It's worth mentioning again. Fast means many things here, fast to create, fast to change the design for clients, and fast in helping you get to development quicker.

Have you ever seen a silk teddy bear. They're nice, soft, smooth and comforting. They take something scary and unmanageable like a grizzly bear, and make the animal manageable, gentle and silky smooth.

In the just-released Beginning iPhone 4 Development, authors Jeff LaMarche and David Mark team up with Jack Nutting to take the ever-growing and changing iOS and break it down into manageable chunks. In this informative and light-hearted read, the authors bring the new edition with updates to key subjects like Core Data, Grand Central Dispatch and iPad/iPod programming specifics. Full of step-by-step instructions and intuitive pictures, Beginning iPhone 4 Development serves as a perfect guide for the novice yet remains effective as a quick reference to the experienced developer. In the end it's all about having fun, making an app you want and not about getting frustrated at trying to understand the idiosyncrasies of iOS. With their latest offering, LaMarche, Mark and Nutting get you on the right path.

I'm done! After a summer of surprises, swings, and roadblocks I finally finished this book, a few months behind schedule, but it's done. The last objective-C book I read was by the de facto in Mac OS X development Mr. Hillegass, (my post) I embarked on the journey of reading a book on iPhone development with the man in iPhone teaching Jeff LaMarche. Jeff is every bit as good at breaking down complex topics and making them seem easy as my .Net home skillet Scott Hanselman. In short these dudes are just smart, but they'll never tell you that and they write some good books.

This book is an easy read and provides hands on examples on how to use many of the tools provided with the iPhone SDK 3. The book is spot on with it's examples, but I'm betting new Objective-C users might have trouble following along when  xCode 4 comes out. xCode 4 is quite a bit different graphically than 3 and may render the step by step instructions in this book out of date.

Overall if you are into programming on the iPhone, this is a great book to start, given you have a base working knowledge of Objective-C and an advanced understanding of programming in general.

 

Error Readout:
error: expected '=', ',', ';', 'asm' or '__attribute__' before 'interface'

Fix:
Added a semicolon.

Explanation:
It's important to remember that this was occurring before the interface tag, which meant it was happening in a file I was importing. In this case it was a header file with an enumeration in it that were not showing an error with a missing semi colon.

Apple expects to sell 1 million to 1.4 million iPhones this weekend, this is excluding the 900,000 pre-orders. It has the possibilty to be the biggest selling product release in history!

http://online.wsj.com/article/SB10001424052748704629804575325661775151320.html?mod=WSJ_Tech_LEADTop

UPDATE: They sold 1.7 million. Apple's most successful product release in it's history.