Yes it's in customs. What's interesting is generally anything coming from China clears US Customs in Anchorage, AK. I would call and be sure your package did not accidentally end up in the wrong place, because that seems odd to me. I've never actually seen an Apple shipment scanned US bound held for Customs in China (in the rare instance we do have an issue and look at an Apple shipment) - this early in the iPhone shipments they almost always come together as a pure Apple shipment.
I've spent 21 years at UPS in management of their international brokerage firm. We deal with Apple shipments a lot. =)