Jailbreak enables you to customize your iDevice entirely. Through editing and installing extensions you can completely change the appearance of your iDevice. 'Boot screen' is the other one you can customize through jailbreak.
Apple logo is the default boot logo but you can modify it with a little tweak.
But if you fail to include animated boot logos from cydia and didn't jailbreak recently on any iOS 4.0+ firmware, then iH8sn0w enables you to do this. The 16 years old boy tweeted on his twitter account explaining that he would soon publish a fix for the known issue.
If you want to locate cool animated boot logo then you can check out Alex's top 10 custom list of boot logos.If you are using iOS 4.0+ and want to have animate fix then you must install it.
Have you ever tried Animate fix?What boot logo do you use?