SmartPost - the shipping service's actual name - has a tracking website, somewhat similar to FedEx's regular tracking website. Upon being notified by RepairClinic.com that my order had shipped, I checked the tracking information and saw that the only entry listed was "Carrier Notification Made". Several days went by, and this was still the only entry listed. I then assumed that due to the cost-savings nature of this shipping option, the tracking entries would be few and far between. Several more days went by - no package - no additional tracking entries. A couple of quick web searches yielded the information that SmartPost shipments could take up to 7 to 10 business days to arrive. I wasn't happy to read this, but I figured my package must have fallen into that lengthy time frame.
On the Saturday following the 9th business day since the package had supposedly shipped, I tried calling SmartPost customer service. No luck; they're closed on the weekend. Then I called RepairClinic.com to see if they had any way of checking if the package had ever actually left their facilities. The woman who answered my call was very helpful, and after putting me on hold for a couple of minutes to look into the matter she returned and, in a slightly perplexed voice, said, "It looks like your package was delivered to another customer."
I responded with a perplexed, drawn-out, "Ohhhhh-Kaaaayyyy???"
She proceed to inform me that she would send out a replacement shipment on Monday via FedEx Overnight, and gave me the replacement order number.
The replacement shipment was actually sent via FedEx Ground, but the results were the same because it arrived the following day, on Tuesday.
From reading more about SmartPost tracking online, it sounds like there are supposed to be additional tracking entries throughout the process, not just the initial "Carrier Notification Made" entry. I'm not sure what happened with the original shipment - if FedEx incorrectly routed it during their stage of the process, or if they handed it off to the USPS and they delivered it to the wrong address, or what the problem was.
At any rate, the experience left me with a rather poor opinion of FedEx Economy/SmartPost, and I will avoid this option in the future whenever possible.
RepairClinic.com was very helpful and I have no complaints with how they handled the situation. I only wish I had called them at least several days earlier, instead of waiting as long as I did!