uxmyths:

There are usability practitioners who completely dismiss the importance of aesthetics, often citing unattractive but popular websites such as Craigslist.

However, aesthetics do have a function. Attractive things work better. Studies show that emotions play an important role in the users’ experience. If a website has a pleasant visual design, users are more relaxed, tend to find the website more credible and easier to use. A positive first impression — usually based on looks rather than interaction — determines the value of the website on the user’s behalf.

Aesthetics also tell a good many about your brand, product or service. It shows that you care.

Read More

jdg:

Core Elements:

Carrier Status bar - 320x20
UIView - 320x460
UINavigationBar - 320x44
UITabBar - 320x49
UISearchBar - 320x44
UIToolBar - 320x44

Data Input:

UIPickerView - 320x216
UIDatePicker - 320x216
UIKeyboard - 320x216

Buttons:

UISegmentedControl - 320x44
UIButton xx37

Fields:

UITextField - xx37
UISwitch 94x27
UISlider - xx23

Indicators:

UIProgressView -xx9
UIActivityIndicatorView - 37x37
UIPageControl - 38x36