A comment prompted this one. I think my response is too big to put in a comment. This is my understanding of the subject.
Do free email account providers collect your personal information? Yes. When you sign up they ask for your real name, postcode and country. Actually, they ask for more than that, but that's the only personal info you have to give (at least with yahoo. I'd assume they are all pretty generic).
Do they sell your personal information. No.
Do they collect information about what sites you navigate to on the net. Yes. They set cookies and check what they cookies has collected later on. Can you prevent this? Yes. Go into your prowsers security preferences and delete any cookies you don't want.
Are there any cookies you would want? Yes. These email providers set cookies to provide a timeout for you email account so that if you forget to log off no one can wander up and go through your email.
Do they collect information about what ads you click on from your email page. Yes. Then they know what products and services you are interested in and will show you ads for similar services next time. They will also make this information available to their marketing department so they can more effectively sell advertising space. So they would say something like "Oh yeah, there's a huge market for pink, knitted dog coats. We've had 327,486 click-throughs on that in the last week!"
Do they capture your IP? Yep, but then anyone can do that. _I_ can do that. Most sites want to have a vague idea of where their traffic is coming from.
Do they read your email. I highly doubt it. This would contravene privacy laws in any developed country, but like our phone conversations, these can be acquired by a subpoena.
Do they capture keywords from email subject fields. Yes. This is good and bad. Good because they use this tool to keep spam out of my in box. Bad because it's something they are allowed to read and most people think all communications are private. Solution: Just don't put anything personal in your subject lines. If you don't want your subject lines used for market research, don't stick product names in there.
My Conclusion: It depends on how gung-ho you want to be about it. I figure that I get massive amounts of storage, an email service I can use anywhere in the world, they don't get as much browser info from me as they would probably like and I don't pay for it. Outside of the net you expose information about yourself all the time. I signed up for a booklover card with a bookstore. I noticed that they spelled my name incorrectly and weirdly. Amazingly I started receiving junk snail mail with the same weird spelling. When people in the street ask you to answer a few questions for research. Do you acquiesce? Lastly, your name, address and phone number are in the phonebook.