​As I am using Yahoo!* weather, I started asking myself, why would that be one of their first mobile apps. 

I mean, look, you'd be hard pressed to put an ad right into the weather app (though you could). You're not going to charge for it - too many free competitors. You're not driving traffic back to other places that are generating ad revenue (though they are trying that in a mobile sort of way.) 

Then, why weather? Well, it got me to thinking about checking the weather. First, it tells Yahoo! where I live. (If I'm responsible, I'm probably checking before I get myself or my kids dressed, so it's telling them what my normal routine is.) If I work in a different city (especially in micro-climate heaven Northern California), I'm probably checking the weather there too. If I'm going on vacation (or thinking about going somewhere), I'm checking the weather there.  ​

​So, without thinking about it, I'm telling Yahoo! a lot about myself with this app. That gives them a lot of information by which they can target stories or ads at me. I like the app, so I'm willing to make the trade. But I'm making the trade consciously. Now, at least.  

If they can get all this from a weather app does Yahoo! shelling out $1.1B for Tumblr make more sense? 

* Full disclosure, I used to work at Yahoo!
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