I would pre-order if I trusted Tiger would be in my hands faster. It really is anyone's guess. I remember with 10.3 people started getting them from Apple a day or two early.
I am so excited about Tiger--pretty pathetic for a grown man, I know--I am going to buy it at the Apple store. I assume they will have tons of copies, so I am going to buy it there.
My experience with iLife & iWork was I pre-ordered it, but it was at the Apple store first. So I ended up buying them both on the spot before the pre-order came. Then when the delivery came, I had duplicate copies, so I sold the second set on Craig's list for a 60 dollar loss. Pretty pathetic, I say.
So I am keeping destiny in my own hands, so to speak.
I'm really looking forward to Tiger. I keep reading about a lot of work which needs to be done, so I hope Apple is taking their time. While I would love it tomorrow, I'd much rather have a solid 10.4.0 release.