Try it for yourself. If you don't like what it has to offer, you can always revert to iLife '06 using the original discs.
One big caveat to that advice: If you have created anything in iWeb, be sure to back up the Domain file before installing '08. Attempting to use '08 to edit '06 websites seems to be a recipe for disaster.Try it for yourself. If you don't like what it has to offer, you can always revert to iLife '06 using the original discs.