I think it was your post in the android forums that sparked my sudden interest in cases and screen protection, after all, it's only a matter of time before that drop or scratch! so in regards to purchasing them, 'sooner rather than later' springs to mind.
I've dropped mine rather a lot, I've actually lost count now... Mine has made bids for freedom onto such forgiving surfaces as carpark asphalt, concrete paths and tiles at home, all from hip to about chest height. I'm so glad I'd bought a case before the phone even turned up! Have been using one since day one and it has saved me a great deal of grief.