No problems, no complaints. I had pre-registered, got a friendly call the night before the release date to let me know they had it in store & to schedule a pickup time, and was in & out in no time on release date. The only issue I had was that I can never get the activation fee automatically waived... I think the first time it happened I just called Sprint and got it waived immediately, the second time I was unsuccessful. It was the only time I've ever had to pay an activation fee in 11 years & I would have pursued it further but life got in the way.
I saw the big warnings other people posted about Radio Shack, too, and I'm a little confused by that. Not only was I happy, but I think that my activation was about as complicated as it gets: because I wasn't out of contract, I had to use my wife's line (which is by itself on a SERO plan) to upgrade. I then had to transfer the phone over to my line which is a part of my dad's plan (who lives across the country). When it came time for my wife to upgrade, I used my sister's line (also on my dad's plan) and then transferred it back over to my wife's SERO plan.