I am now a 100% believer in using starters. I just brewed an ESB (modified Fuller's clone) and used WLP002 with a 2L starter. OMG! That stuff took off within a couple of hours and has been one of the most vigorous fermentations I've seen to date. It actually blew the cap off my carboy.
For anyone out there questioning the need for a starter, let me just say, do it. Sure, you can brew without one (I do know what the White Labs vial says), but I wouldn't recommend it, not after seeing the difference between using a starter and not.