When I woke up at 10am (yes, I slept in :P), I noticed that, about 2 hours previously, I received the record search in my email.
I was concerned about a few things, but after creating a thread on VJ about it, I was reassured that everything was most likely okay. So, I printed it out, included the USCIS letter on top, and stuffed it inside the provided envelope.
I then proceeded to the post office here in town. I of course wanted tracking, so the envelope was put into a clear Priority Mail envelope. Not only would I get tracking, but it'd shave off one day, compared to First Class mail. Cost me an extra $5, but I think it's worth it.
So, it should arrive on Thursday. Now, to just wait. I'll post again once it arrives at USCIS in California.