It doesn’t force you to click the ad. After you wait for the countdown there’s a link to close it. Clicking the ad doesn’t close it either, you have to wait for the Close link to appear. It’s just like those ads on free mobile apps and games, where the (X) button is disabled until you wait a certain amount of time (usually while a video plays).
I realize it’s a bit obtrusive, but it only pops up after every 50 homepage actions (searching, paginating, sorting) and only lasts 45 seconds. For most people that might mean once every day or two, for heavier users it might be a couple times per day. If you don’t want to pay any money to use the site I think it’s fair to give up 45 seconds of your time every once in a while so that advertisers can support the site instead.
We have users who do thousands or even tens of thousands of searches a year, make a lot of money from the data, and don’t have a membership. That’s because we give a lot of functionality away for free. Rather than changing the site to only allow people to do a few searches a day for free like Estibot, or otherwise restricting the site for free users, we’re creating new advertising opportunities.
If it bothers you too much you can always pay as little as $60/year to get rid of them, and get lots of other benefits as well. Otherwise you’ll have to see some ads.
I’m not planning on any other changes, I think we’ve maximized what we can do with ads on the site with this, all the auction widgets, and featured listings.