It wasn't long after our review of Uzu for iPad that developer Jason Smith got an e-mail from Apple. It wasn't an app rejection, a shipment delay, or a question about his developer stats. Instead, Apple wanted promotional assets for Uzu, as the company was interested in featuring it on the App Store.

This scenario plays itself out weekly, and receiving an e-mail like the one Jason got can mean a number of different things. It might mean nothing: Apple is interested, but the company eventually changes its mind. It also can mean you are going to get a small feature spot. Occasionally, it means you might get a large feature spot at the top of the iTunes Store. If you are lucky, it may mean the app will get an "App of the Week" slot in some far-away country. If you hit paydirt, you get the coveted "App of the Week" moniker in the US App store. That's what happened to Smith.

Curious as to what effect such promotion had on an application, we contacted Jason and asked if he would be willing to share his sales numbers for the time he was featured. He agreed and was nice enough to send us the data for his worldwide sales numbers for a period of just under 30 days.

To understand the effect that the "App of the Week" promotion had on the app, it's important to understand the sales record prior. In the week leading up to the event, Uzu was averaging 365 sales per day for a total of just under 2,000 sales per week. After Apple's cut, that works out to a gross of about $1,400 per week.

It should be noted that 2,000 sales per week is probably a bit inflated, as the week began right after a somewhat large influx of press. As you can see by the chart below, sales numbers slid as the week progressed, leading us to believe that average per-week sales were actually much lower.

Once the "App of the Week" feature began, sales immediately skyrocketed to more than 10 times the previous day; in one day, more sales were made than the previous week combined. The application peaked at 5,312 copies sold on July 25, reaching number two in the iPad paid apps chart. The week saw a total of 25,913 sales, for just under $18,000 in revenue. At the somewhat inflated rate of the week prior, Uzu earned in one week what it would have taken 13 weeks to achieve.

Once the "App of the Week" run came to an end, Uzu sales numbers slowly declined. While one might think the sudden lack of Apple's golden touch might make for an instantaneous drop in sales, that didn't happen. Uzu was visible on the iTunes front page in the top 10 paid app slot for several days, leading to a slower decline. The week after the promotion ended, sales totaled just over 6,100, or an average of about 872 apps sold per day.

As more and more iPads are sold, developing for the platform has a greater potential to pay off. Figures from various developers seem to show that universal apps can bring in a revenue increase of anywhere from five to 20 percent over an application written solely for the iPhone. Whether those numbers are enticing enough for developers to do so, though, will remain to be seen.

(Thanks to Jason Smith, creator of Uzu, for allowing us access to his numbers. Jason is currently working on improvements to Uzu and is also expected to launch Little Uzu for the iPhone in the coming days.)

Update:Little Uzu is now live on the App Store (iTunes Link).