Attention to detail is very important in the user experience for mobile apps. Here’s an example (courtesy of Daring Fireball) from the iOS email program. It’s a small thing, but these behaviors add up to a very polished whole.
This blog, ‘The Invisible’ is brand new, with just two postings, but is a very promising look into the little details which drive the fit and finish of user interfaces. The first entry, about tab closing in Google Chrome, is also very enlightening.