The iPhone’s music app (the iPod app) has an interesting horizontal variable slider. What makes it interesting is that while it looks like a typical UISlider the further away from the slider you get vertically the finer the adjustment made when you slide your finger horizontally.
This is interesting functionality, and allows users to gain finer accuracy with a smaller scrubbing speed when making adjustments. Recently, Ole Begemann was responding to a question and created an open source, MIT lice’s nsed, replacement slider which you can drop into your apps that provides functionality similar to the slider within the iPod app.
You can find a video displaying the functionality, the download links for the source code, and an in-depth explanation of how the code operates on Ole’s blog here:
OBSlider, a UISlider subclass with variable scrubbing speed
It makes for a very handy piece of code to have around.