Can you think of any good reason to not send it in? If you ever have a problem with it, you won't be able to prove your date of purchase or the ballast's serial number for warranty service. The cost of a stamp is a pretty cheap investment if you ask me.
I don't know why anyone wouldn't send it in. I just got a IceCap ballast also and I sent mine in. Sure sending any registration may result in some junk mail but it would be worth it if you ever have problems with the ballast.
