FIH: Except for the fact that, here in California at least, guns are taxed at the time of purchase. This is the same as purchasing a motor vehicle, wherein you pay a tax on the sale.
Also, you have to fill out a BATF Form 4473 prior to purchase. While not a registration per se, it is a document filed every time you purchase a weapon at a licensed dealer.
I’m all for universal background checks. I’m just not too keen on the gubment having a centralized registry. If the revelations about IRS misconduct, NSA snooping and the AP fiasco have shown anything, it’s that the US government isn’t all that deserving of our trust when it comes to our personal information.