Say, from my gmail address? Like if I emailed someone, could he use the IP address to find out anything about me? My address, phone, real name, any of that?
I dont think they could get your IP through an HTTP email service but in the world of computers anything is possible. Could they? Possible, will they? no. Google does have quit a bit of information on you but even they usually dont give it up sometimes even going against the courts. If they have an IP they could find out your ISP, and about where you are located. If you were involved in something like child porn and the authorities found your IP they could contact your ISP to get your address and name etc. But just from sending an email? No, i would be more concerned about someone going through your snail mail, mailbox.
About all you can get from an IP address on its own is a vague geographic location and the name of the entity that owns the connection.
To clarify, you’d be able to say “This came from an SBC DSL customer, and they appear* to be in Nevada.” You would not be able to take an IP and say “This came from a person with a Mac on the west side of Fremont, California” much less “This came from Dan, and they live at 345 Whipple Drive in South Tiptoe, New Mexico.”
*Depending on what system you query, my own semi-static IP at home either resolves to my registrar in Virginia, or to my ISP in Northern California. You can’t get much more useless than that. 
The situation gets even more tenuous for dial-up users or people with dynamic IP broadband service, which is to say, most people. (Static IP service costs more, so most consumers don’t get it.) In this case, each time you dial in or connect up with the broadband, your ISP hands out the next-available address from the pool of addresses they own.
It’s worth noting that GMail is one of the few free web email providers that obfuscates originating IP addresses shown in the email headers.