I've mis-used databases just as you describe. And continue to do so. That's fine, I'm an amateur, and I never needed to handle databases larger than a couple thousand rows. I could probably get away with tens or hundreds of thousands of rows before running into problems.
Now if I were to develop something that needed a billion rows - that's a different story, and I do know my current approach won't work and I'd have to learn a lot about databases to pull it off. And submitter is obviously trying to do that (or at least something that needs a few rows and hoping it grows larger than Facebook and Google combined, so he needs scalability). Also I believe submitter doesn't really know what he's talking about.
If you really need to be able to handle that kind of data sets, and have even just a subset of the skills needed, you don't come to Slashdot for advice. You'd know who to ask - a friend or colleague who does just that.
So submitter may have big dreams, he almost certainly doesn't have the skills to have even a fighting chance of making it. And with that I don't need the actual database management skills, but the skills of knowing where your weaknesses are, knowing who can fill those gaps, and asking those people (maybe by having a discussion over a beer, or by hiring them outright).