I've had mine almost a week now. So far no issues with reception. I'm left handed and before I put the case on my phone could absolutely see that the reception dropped when I held it like I normally would.
I'm to "risk averse" when it comes my phones to NOT have a protective case on them, so with the case, no significant reception problems. It's certainly no worse than my previous iPhone 3G, and I've noticed no increase in the number of dropped calls. All dropped calls have been attributed to my relatives calling me from basements.
I mean seriously, come on, stop calling me when you're in the damn basement people...