One thing that's frequently annoying me when using my Android (OS version 2.1) phone is the fact that there is no instant feedback when using the slider control. Earlier versions of Anroid used to have more of these types of issues but like Brenton Klik points out in his article about scrolling, some of the problems have been solved.
An example of mitigating the problems with feedback and touch interfaces is the soft keyboard. When typing the letters pop up in a box above the pressed key. That way the problem of your fingers blocking the view is somewhat resolved.
However the sliders do not have the same built in feedback. When using the sliders it is quite hard to determine what you are pointing at, especially if you are trying to select a position on the slider that is close to the edges of the screen.
But the solution is quite simple. If you were to combine the feedback from the soft keyboard with the slider control you would end up with a slider control that provides instant feedback (like the picture to the right illustrates).
There are already implementations that does basically the same for the web. That means that if you are developing web applications for mobile devices you can solve the problem right now. Hopefully Google will pick up the ball and implement a similar solution in an upcoming Android release.
