It's inevitable that with new operating systems come new bugs. One widely-reported bug has affected a noticeable chunk of laptop Mac users who've upgraded to OS X Mountain Lion: some users are reporting steep declines in battery life. A poll at Engadget shows that over 7400 of nearly 17,500 respondents who've installed Mountain Lion (42 percent) say they've noticed a definite and discernible drop in battery life. A similar poll at RazorianFly suggests that the 2011 models are disproportionately affected, but that may be sample bias.
Battery problem reports came out last year when OS X Lion launched. The problem with these bugs is it's nearly impossible to predict which systems will be affected or under what circumstances; my Early 2008 MacBook Pro has had no observable loss of battery life under Mountain Lion, but a brand-new MacBook Pro may well see battery life declines of 20 percent or more. No one has tracked down a specific cause or a fix yet, including Apple. However, it's safe to assume this will be a top priority for the forthcoming 10.8.1 update, so don't start sharpening those class-action lawsuit claws just yet.
Far more concerning is the way "Save As" works in Mountain Lion. You'll recall that Mountain Lion brought "Save As" functionality back to OS X, which spared us from a year of workflow-breaking "Duplicate" then "Save" hoop-jumping. Fellow TUAW blogger TJ Luoma even figured out how to change the menu commands around so "Save As..." showed up by default instead of "Duplicate" in the systemwide "File" menu.
Unfortunately, it turns out that Mountain Lion has answered a question no one thought to ask until now: When is "Save As..." not really "Save As..."?
The answer is surprising and somewhat distressing. As Mac Performance Guide notes, the "Save As..." command in Mountain Lion saves changes in your new document and the original document. In my own testing, the reason seems to have something to do with Mountain Lion's auto-save features. Initiating and completing a "Save As..." command will automatically close the original document and leave the new document in its place. The simple act of closing the original document triggers Mountain Lion's auto-save feature, meaning the next time you open the original document, those changes will still be there.
This could be a potential nightmare for document version management. My own testing in TextEdit and Preview documents showed that Mountain Lion's handling of the "Save As..." function wasn't at all what I've come to expect from nearly 30 years of using Macs. Anyone not familiar with the esoteric intricacies of Mountain Lion's auto-save behaviors (in other words, the overwhelming majority of users) is likely to fall into a panic the next time they open their original and supposedly preserved document only to find something else entirely in front of them.
Mountain Lion's use of auto-versioning means you can always revert the original document back to its pre-"Save As..." state -- but we shouldn't have to, and counting on everyday users to be capable of navigating through the Versions interface to find their original document seems foolhardy at best.
No. Just no.
All of this means that the triumphant return of "Save As..." to Mountain Lion has turned out to be not so triumphant after all. The way the command worked in the past, your original document would be preserved without edits and would be waiting for you in its original state the next time you opened it. The new behavior in Mountain Lion is more complex, far more confusing, and has far more that can go wrong with it.
Some people might say that the old methods of document management and versioning are old-fashioned, and the new way is better. As someone who regularly works on complex projects demanding meticulous version tracking, I respectfully disagree. This isn't necessarily a "bug" in Mountain Lion, but it is conspicuously incongruous behaviour -- and it's also something Apple can improve for users, if it chooses to do so.