Day 4, learning Objective C
I completed my custom control yesterday - it's a simple knob style control. I feel I understand the basics of Core graphics and implementing a UIControl from scratch (including getting touch input, sending a an 'event' when someone interacts wwith the control, etc). To reskin an existing UI Control, you would just subclass it and override any methods you want to change. This may include some of the input methods if you want to control how people interact with it. If you want to change the look/feel then you can override the drawRect method. Core Graphics is very similar to other UI frameworks I've used, such as LibNUI, Swing and Juice, so no troubles there.
Today I started working on an RSS reader to learn some more of the specifics about working with the UITableView component, which is probably the most used component of all.
Some more good resources I came across this morning: