Windows Phone is great (in my opinion). But it lacks any sort of customisation apart from tile colours and either a white or black background. The one thing I really missed in Windows Phone was using custom tiles or tile backgrounds. The Windows Phone Hacker team have created a tool to enable you to do just this.
As you can see this is a tool for Windows on your pc. You basically create the theme on your pc and transfer it across to your device. There are two criteria to make this work though. You must have a Mango device and you must have an unlocked device. To get unlocked you can go to the ChevronWP7 site and give them some money and they will unlock your device. The video below pretty much shows you how to create the theme and how to apply it. I am quite excited about this and once my device has been unlocked I will be giving this a go.