Jay Freeman, the author of Cydia, has just released an update of the awesome Winterboard application. The latest update empowers Winterboard to load themes much faster. Frankly, I do not experience much lag after installing Winterboard on iPhone. Some readers, however, mentioned there is a performance issue when loading theme with Winterboard. This recent update should probably fix the performance issue. You can download or upgrade Winterboard from Cydia.
Flashing Christmas Light for Winterboard
On top of the 3 great Christmas theme for iPhone, you can even add flashing light around the screen. Download it from Cydia (source: http://apt.modmyi.com) and show it to your friend.