Apple's aqua theme for Mac OS X has been with us from day one. Back in 2001, when the new operating system was first released, it was quite a step up from most other interfaces, but many people were also a bit distraught over the loss of Mac OS 9's Platinum look and feel. We're 8 years down the line now, and it's actually quite clear that Mac OS X' look is in a transitional phase.
Aqua was characterised originally by lots of glossy, watery elements, as well as subtle translucency, giving the impression of interface elements being droplets of water. Over the years, however, Apple has toned down the glossy and the shiny, preferring a softer and more matte look. The biggest hint yet that Apple wants to ditch the Aqua appearance came in Leopard when the company replaced the traditional glossy Aqua folder icons with the matte ones. The toning down of the glossy can easily be spotted by comparing a screenshot of the Mac OS X Beta to one from Leopard.
The side-effect of all this is that Mac OS X' interface is currently a bit at odds with itself; does it want to be glossy and shiny, or soft and matte? Several elements have been made softer and more matte, while something as prominent as the dock has had its glossiness slider set to "bizarre".
The new interface of Snow Leopard is supposed to fix all this, by moving the entire interface to the soft and matte look. For instance, it is said the Aqua blob scrollbars will be a thing of the past, replaced by ones similar to those of iTunes.
I would welcome the changes, because I believe Aqua has served its time, and right now in Leopard it all feels a bit... Incoherent. Obviously, as is always the case when it comes to Apple, none of this is confirmed, so it might as well be absolute bogus. Still, AppleInsider has a relatively decent track record (at least, when compared to most Apple rumour sites), so it might actually still be true. It is said Apple will demo the changes at the yet-to-be-announced WWDC09.