I get them as I have a rediculously AWESOME Verizon Wireless account manager. She knows that if she gets me a Pre-Prod device, I will test the crap out of it and give her both valuable feedback as well as create some buzz... at least that's what I believe.
I've been able to test the Thunderbolt, Bionic, and also some Blackberry and Windows Mobile phones in the past year.
As far as rooting goes, I am crazy with my ROMs! I think the Thunderbolt has the most options out there as far as ROMs, kernels, etc. out there. (Except for perhaps the Original Droid...) I sincerely hope that the Vigor (or whatever it is to be called) will have the same Dev support!