I dont see the need to preorder for a few reasons. Just my humble opinion though.
The popularity of the Evo is undeniable, and there were shortages. But with the galaxy s2 being this year's "it" phone and the sensation incoming. I think the demand might be a little less. That along with the fact that many people have decided that they simply dont want this because of the 3d (agree or not, it turns many people off to the device) may give it less selling power than its predecessor.
Also, I find it a little jumpy to preorder something that hasnt been reviewed at all yet. The battery or other key features might suck. Oh and it doesnt even have a date yet.
All of these things make me confused why so many are eager to preorder. But thats me. Dont get me wrong, I am very interested in this one, but not enough to go through $50 down for it.