I expect a return from hibernation to be slightly costly compared to a straight boot.
The speed of Ubuntu bootup and shutdown is so comfortable that I always choose to shutdown.
However, I can understand the need for hibernation, and also the conditions when one would usually use it -- leading to the related slower restore...
You could try
TuxOnIce (formerly known as Suspend2) is an implementation of the suspend-to-disk (or hibernate) feature which is available as patches for the 2.6 Linux kernel. It was formerly known as 'swsusp'.
UbuntuGeek article ref,
Tuxonice is an alternative way to hibernate your machine than the standard ubuntu power manager way. It generally claims to be more configurable and flexible than the standard method, with faster hibernate and resume times.
References: Wiki and HOWTO.
Also you may want to read this.