An updated tweak has been released in Cydia today called "Animate Fix for 4.x.x/5.x.x" which allows you to use the custom bootlogos that were introduced in the 4.2.1 jailbreak on iOS5 devices! Using this tweak is simple. Install "Animate" from Cydia(even though it still currently says that it's for 4.x.x only). After you've installed Animate make sure to install "Animate Fix for iOS 4.x.x/5.x.x" which is needed to use custom bootlogos on iOS5.

After you have installed these two packages, you are free to us any of the custom bootlogos in Cydia that are compatible with Animate. To select which bootlogo you want, simply open up your settings app and go to "BootLogo" and put a checkmark next to the name of the bootlogo you want to use. Upon rebooting you will see your custom bootlogo, of course you will always see the standard Apple bootlog first as with previous versions of Animate.