This was the sort of info I was looking for. I'm not against change per se, but want a good reason for doing so. If moving to 10.8 has actual benefits insofar as working with LR5, then I'm prepared to move my anticipated upgrade to sooner rather than later. Thinking about picking up the 10.8.4 download to check out on my i7 MBP.
The biggest reason to upgrade your OS (if you don't really care about the shiny new end-user features) is when the applications you rely on require you to upgrade the OS, honestly. With OS X especially, each of the last 4-5 releases has reworked a number of things under the hood that allow application developers to make better, faster, more stable software. Once developers start leveraging that, they can only support back to the OS version that includes that API.
For developers, they're forced with a choice: If they're to support older OS versions they have to have a more complex code base, and often duplicate a lot of the functionality that Apple offers, or they can just use Apple's APIs and cut off older customers. "Typical" for many developers is to support a couple versions of OS X; some are still supporting 3 (10.8, 10.7, 10.6). With a new version expected to be announced at WWDC I'd expect that more folks will start cutting off 10.6 support over the next few months, as Adobe has done with Lightroom.