After reading through all the experiences here and over on xda, I will admit I was concerned about how things were going to go, but it has, so far, been one of the better Best Buy pre-order experiences I've been through.
Hubby and I are both with Verizon, on the same account. When we pre-ordered several weeks ago, they wouldn't allow us to pre-order 2 black GN4s, and said that was a Samsung/Verizon issue and nothing Best Buy could do about it. We begged, pleaded, etc. but to no avail, their system simply wouldn't accept a second black pre-order on the same account. DH said he'd be cool with trying the white one out, and if he wasn't happy, he'd exchange it. Ok, cool, we leave with one black and one white GN4 pre-ordered.
Fast forward to today - we got the email that the black one was in and ready for pick up, but no sign of the white one. At the store, we waited in line for about 30-45 minutes before being helped (and we got in at a good time, in the five minutes after we got there, about 12 more people showed up, mostly for iPhones). Our Best Buy guy walked through the upgrade quickly, and I am the happy new owner of the black GN4. Traded in a $30 Kyocera phone for the $200 gift card without a problem.
We asked if, by any chance, there were any unclaimed black ones, since the white ones haven't come in yet. BB guy took my husband's name and phone number and said he'd be working through to next week, so if any black ones became available before the white we pre-ordered came in, he'd give us a ring. He mentioned that they only had 6 black pre-orders at the store, and may have 10 in stock, so we're keeping our fingers crossed for tomorrow or Saturday. Still not clear on why, if there were extra, we couldn't nab one today, but he was ridiculously helpful, efficient, and competent that I didn't push the issue.
Overall, it went well. Still frustrated about the white/black issue, because if we'd been able to pre-order two black ones, he'd probably have his phone too, but supposedly that's not a Best Buy restriction, so I can't say they did anything other than everything they could for us.