Ad impact

About 2 years ago I promoted my apps with ad banners on some websites and my conclusion was that it doesn't work that way. So why did I do it again?

In January, after working full time on my apps for about 4 months, app sales remained flat despite multiple major app upgrades. I decided to give online ads another try.

What did I do differently?
1. I carefully selected just 2 sites with a specific target audience in mind.
2. A friend of mine (a marketing guru) helped in determining the ad content
3. I hired a designer to make the ads
4. Each ad promoted 2 apps (using animated GIFs) instead of 1
5. Ads were only shown to people who own at least 1 iOS device

For a period of 6 months, Scotty and GeoTagr are promoted on iPhoneography, the no. 1 site for iPhone users interested in photography. In April, PhotoMeta and GeoTagr were promoted on Digital Photography School (DPS), a wildly popular site targeting advanced amateur photographers. Ads on DPS (250 000 impressions) were only displayed on iOS devices.
Both ads had a clear impact on app sales, but not the huge spike I was hoping for. I spent about 3000$ on the ads (that includes the designer) and that's roughly what I made on my apps the past 2 months. It's impossible to measure what percentage of those sales are a direct result of the ads, but I assume that in the long term the ads will have a slight positive effect on sales.