I know this is a late response (congrats on the second interview!!) but considering others might read: I work in HR and I currently have 15 open positions I'm working on. I want to fill them all yesterday but I just don't have the bandwidth since recruiting is only a part of what I do. I work through them as quickly as I can but if you applied a week ago and haven't heard it doesn't necessarily mean you've been screened out. I just might not have had the chance to review your app yet. Really, lots of things can slow the process. (OP, you obviously understand this so I'm just reinforcing.)
Keep this in mind when you check in too. One phone call or email is fine but if you do it repeatedly, you're just adding more work to the person's plate and they won't think happy thoughts when your name comes up. Mostly I don't care if you send me a follow-up thank you email but if you do, make sure to use proper grammar and spelling - READ IT AGAIN BEFORE HITTING SEND - so that you don't do more damage than good. (This is especially important for professional positions where you are representing the company when you communicate.)
Also, this is OT, but there are SO many reasons that you might not get a job. Only a few have to do with you. So don't take it too personally if you don't get a call. On the other hand, if you keep not getting called/back, ask for input from someone professional on your interview prep/skills/outfit/resume.