Apple has delayed the mandatory sandboxing guideline for Mac App Store apps once again, amidst criticism that the guidelines are unclear and that sandboxing will do more harm to developers than it will do good — for the developers or for the Mac platform. TUAW's Erica Sadun has a good summary of the deadline and why people are kicking up such a fuss about this — with some developers already saying they're going to pull their apps from the Mac App Store due to the sandboxing policies. With Mountain Lion, it seems as though Apple are moving to an annual release cycle for OS X. This and other thoughts are in the Anandtech summary of a few changes in Mountain Lion, which includes a few notes about the new Safari 5.2 (also available for Lion), as well as software updates moving towards the Mac App Store. It's worth a read.
If Notification Center is the first-party solution to notifications on the Mac, that doesn't necessarily make Growl inferior especially as non-Mac App Store apps won't be able to access Notification Center. Hiss changes that, sending normal Growl notifications to Notification Center like nothing ever happened.
Rotating screen savers, either from your own iPhoto library or just a collection of images on your hard drive, are great. OS X Daily has a tip you might be interested in. It means you can make your own custom screensaver from a Flickr RSS feed, having beautiful custom images as your screensaver.