For me on 10.8.3, with 5 tabs open including this page, it's already over 600 MB (Safari Web Content and Safari together). I don't know what these ******s Apple engineers are doing as it's has been ages but they can't seem to fix bugs in ML. I also noticed that with Auto Proxy Discovery option enable (I have to have it because of my Institute wants this), my rMBP becomes unresponsive for hours and I have to forcibly reboot the system. This is so ****ing annoying and I'm terribly disappointed that these bugs are still not fixed!