Google has been fine-tuning its mobile in-browser Gmail experience on the iPhone and iPod Touch for years, and over the course of time, the addition here and modification there has added up to a very usable in-box experience in the spirit of Gmail on the desktop, if not its identical feature sets and dimensions.

This week's tweaks focus on iPhone and iPod Touch handsets running iOS 4 in English. They nail down the design of the navigation menu, which Google has been experimenting with on its iPhone-optimized Web site for the past few weeks. Now, the toolbar is fixed in place while you scroll, rather than following after you scroll through a message or the in-box.

Google also performed some back-end tune-ups on the scrolling speed to cut out the lag time between the motion of your finger and the motion of the in-box contents. We won't deny it: there's no delay.

We'll still use the e-mail in-box on our iPhone 4, but we will say that the mobile Gmail experience is improving, one tweak and turn at a time.