Over the past couple of weeks Google has slowly updated the Gmail web application when you visit gmail.com on your iPhone. When visiting gmail.com on your iPhone using the Safari browser you will notice a couple of improvements to the Gmail interface.
The first improvement is that scrolling through your messages is now snappier before it would tend to hang up. The second enhancement is the toolbar at the top, it stays with you as you scroll.
I can say these changes are very welcome and it will make it much easier to manage my mail on my iPhone. The built in mail app does not satisfy my needs when it comes to Gmail. Google says they will continue to make improvements to the Gmail application on Safari. I look forward to seeing any change that will improve the functionality and usability of Gmail on my phone.
Source: Gmail Blog