Advertising in general isn't over-rated and can get a great ROI. I just don't think it's necessarily the best tool for a web design firm to use.
If you're leaving printed collateral with a receptionist or gatekeeper without at least getting the decision-maker's name, you're probably wasting your time as well as the cost of the printed piece. The gatekeeper may be polite, and even tell you she'll pass it along to the boss, but 9 times out of 10, your information winds up in the trash.
You need to get access to the decision-maker. If he or she is unavailable, try to get the name so you can follow up with a phone call. Befriending the gatekeeper is also a great idea, because you can get some information about their marketing.
When you do call back, don't even ask "did you get the information I left?" because that's just awkward. If the gatekeeper revealed anything useful, say something like, "I stopped by on Tuesday and spoke to your receptionist, Susan. She mentioned that you weren't happy with the quality of leads you're getting from your website. If you're open to exploring other options, I'd like to show you how we've helped other local companies improve the quality of their online leads and increase their conversion rate. Do you have time to meet one day this week?"
Of course, you can come up with a script that fits your offering. But the point is, you need to talk to the decision-maker, clearly communicate the value you provide, and ask a very direct question like, "Is that something you want?" or "Can we meet sometime next week?"
In reality, you're going to wind up speaking to decision-makers about 10% of the time, and (if you're good) close only about 20% of those. And that's only if you're persistent.
For those that turn you down, figure out how you can drip market to them. Send them a newsletter about web marketing, refer someone to their business, things like that. If you stay on their radar, you'll be the first they'll call or refer someone to.