I bought a mid 2012 Macbook Pro 13 i7 machine that had Lion on it. Upgraded to Mountain Lion and saw my battery performance go from nearly 7hrs under Lion to just over 2hrs under ML. I read several threads and tried all the SMC/PRAM resets, killing email accounts that I don't use much, turning off iCloud, etc. to no avail. They only made a marginal difference.
I was about to call Apple as a last resort, and then look at returning this machine since I'm still inside my return to BestBuy window.
On a whim, I started closing apps one by one that automatically launch on start up. After closing SugarSync, most of my battery performance came back. Closing DropBox helped some as well. Now, it appears that pretty much all my battery performance is back and possibly a bit more than before with Lion.
I haven't tested this for days or anything, but for the last few days I've only been consistently getting a little over 2hrs of performance on a full charge. Now, as of last night and this morning, I'm getting at least 7hrs and sometimes showing over 8hrs left. I've only been running Safari and Mail, but just closing SugarSync and DropBox seemed to have drastically improved my battery performance under Mountain Lion.