No, Apple has not released this publicly but few things are leaked, as usual. Mac OS X 10.6 Snow Leopard related videos were being shown on Youtube and also a few sites sharing the leaked screenshots and features of the Snow Leopard. And here is most of it taken from a Portugese mac blog -

Finder in Snow Leopard -

Trash had no option to restore the file to the place from where it was deleted. The “Put Back” option in Snow would help you restore to the same place rather than dragging out the files and restoring them to a newer place.
Here is a screenshot -

Resizing the icon size in any folder was previously through its View Options[Shortcut Command + I], but now at the bottom right of the folder there is a slider which makes it easier to change the icon size and customize it in every folder you need. Screenshot below -

Scroll bar on the visualization of Stacks in “Grid” and navigation by folders. This is done with the help of core animation and the normal Leopard does not have this option. The opening of folders is in big folders, but in Snow its in stacks.

Betterment of the Services menu in the Preferences window.

A whole new panel of Keyboard and Mouse preferences with more options, seen in Snow Leopard.

Screenshots get better name with all the information like time and date of recording.

Quick look gets better with preview of videos, and also PDF files as in this better version of Leopard. In the screenshot below, the video preview is shown in Quick Look.

Quicktime player -

The new quicktime player has a lot better interface with black and more basic background and the version is 10.0, build 14.2. Screenshot below -

Edit menu has a trim option, and this is claimed to be similar to the iPhone 3.0 OS feature. This can be done with shortcut Command + T. Sharing with iTunes and MobileMe gallery is also possible through Quicktime player.

There are quite more features which you can all view here.
Images source macmagazine.com.br!