I had this issue for several weeks with my mid-2012 MBA after installing Yosemite. Just like with you, this showed me that "launchd" was the culprit . I talked to some tech friends who explained that launchd is a little program that automatically launches other apps, sometimes in the background, for various reasons. Up until last week, my solution was to reboot the machine anytime it got hot (several times a day). It was a huge pain, and I was borderline ready to give on on Apple having still not seen any official response to this issue that seems to be plaguing many users. Here's step-by-step what I did to resolve it.
1. Open Activity Monitor by typing "Activity Monitor" in the spotlight search. This confirmed launchd was the memory hog
2. Open a Finder window and type select from the menu: Go > Go To Folder (or simultaneously press CMD+SHIFT+G keys)
3. At the prompt, type "/var/log" to access the machine's folder that contains the log files
4. Sort the folder by "Date Modified" and look for the most latest file called "system.log"
5. Double click the file to open it in the Console app
6. Scroll all the way down and see if any lines contain "error," especially repeated lines going back as far as when you noticed the machine was hot.
For me, the culprit was Adobe Pro 9. Apparently this program would try to update itself after I upgraded to Yosemite, but the install update application wouldn't run correctly in Yosemite, so lanchd would try over and over and over again to launch the install application, getting stuck in an infinite, very hot, loop. I deleted Adobe Pro 9, and now everything is back to normal. I don't need Adobe Pro any more, but if I did, I would just get a new version that is compatible with Yosemite.
I hope this helps,
Omar