Four months ago, I submitted the Speed Anatomy (free version) to five alternative android app stores to evaluate their viability. I figured that I would later do the work to get the pay versions in the stores that generated enough free downloads. Unfortunately, none of the stores are currently very good. The stores I published in are: Mobango, AndroidPit, Appoke, AppsLib, and Getjar.
In the past 9 months, Google's Android Market has generated on average over 3000 downloads per day (dpd) for Speed Anatomy(free).
Here are the numbers for the alternative stores (past four months):
AndroidPit: 28 dpd
AppsLib: 6.8 dpd
Mobango: 2.5 dpd
Getjar: 1.8 dpd
Appoke: 0.4 dpd
Even the best alternative app store generates less that one percent of Google's Android Market downloads. In my opinion it is probably not worth the hassle to publish in these stores except maybe in AndroidPit and that's just because they have an excellent site with great UX and features for developers that make the process really easy. In term of site design, usability and features, AndroidPit is probably better than Google.
Another interesting factoid I have since Getjar gives download numbers by country, is that the majority of their downloads come from Iran: 69 versus 39 for all other countries in the past two months. I have no clue as to why.
So that's my experience with one free app on six app stores.