Today I took a look at the information you're required to supply before Yahoo, Hotmail, or Gmail will give you an email account:

Yahoo	Hotmail	Gmail
* First Name * Last Name * Zip code * Gender * Industry * Job Title * Specialization * Birth Date [] Send me special offers from selected Yahoo! partners (checked by default)	* First Name * Last Name * Language * Country * State * Zip Code * Time Zone * Gender * Birth Date * Occupation [] which of 40 newsletters you want to receive in your inbox [] which of 55 topics interst you, so that 'featured offers' from Hotmail partners can be delivered into your inbox	* First Name * Last Name

That's a whole lot of data the other guys want, and they use it to target information. Yahoo admits in their privacy policy that they provide it to third party partners for marketing purposes.

Google, on the other hand, explicitly states: "We will never rent, sell or share information that personally identifies you for marketing purposes without your express permission."

For the curious, I'll likely have some more Gmail information to post tomorrow, so you might want to check back, or grab my RSS feed to keep up to date.