Wiki2Learn has plaid around with some free ads we got for Google Adwords. @ruphy can say more about it. We should test this for other programs by KDE or KDE itself as well. Lydia and Riccardo have access to the account to start campaigns.
yo, just seen the notification :-)
a couple of facts on the grant we have: we have google ads just for the search product, and we can only link to pages on our domain (so we can't link directly to the google play store). we've noticed that a campaign needs serious time investment in order to be successful (you can't just expect to throw a link in the system and have it work everything out by itself). It's possible to get some value out of it, but you do a very careful study of your public, and later need to have daily adjustment of the ads, cpc, keywords, and landing pages.
Also consider that the money seems like a lot, but advertising (esp. untargeted advertising) is really really expensive (1.5/2 USD per click). When we were just testing the system out, and tried to simply draw traffic to our website at full budget, we would get no more than 2k visits per months, with a bounce rate of more than 85% (so 300 visits spending more than 10 seconds on our site).
Aggregate data show that it costs about 35/40 USD to acquire 1 user which does at least two clicks on the website.
Now, after five months of optimization and a student "full-time" on it (doing optimization work as part of a master thesis) we're improving, but we're still at 75% of bounce rate for most content, which goes as down as 70% for very targeted one.
Conversions have increased, and we have now (at full budget) about 60 new users per month (with a very very low contribution/registration ratio: the number of users who made one edit after registering (since november) is about 10).
So in general, I can help, but we need serious thoughts about the audience, to define a campaign, and possibly someone who can optimize this as a full-time duty. This kind of marketing is quite hard...