Finder will be replaced with an app that manages files in stacks based on spotlight meta-tags (Good bye to folders forever!).
I agree with this except for the
replaced part. Stacks will make a great
addition to the Finder. Folders aren't going anywhere. Ever. The user's reliance on them, however, most likely will.
Along those lines, I expect Leopard to let you assign your own tags to files arbitrarily. This should not be at the Spotlight level, but rather the file system level. HFS+ has support for this, and even Tiger has the ability to do it, although it's not used. I hope Apple will use file system metadata more and the Spotlight database less, because the Spotlight database is a nightmare in many ways. Ideally, Spotlight should only be used for caching data that can be re-created whenever needed (basically, as a time-saving measure). For instance, you can re-determine the size of a JPEG based on the file alone if the Spotlight database is damaged/erase, but you CANNOT re-determine the URL of a downloaded file, which Safari currently stores with Spotlight. This leads to unexpected data loss in many circumstances. Spotlight is not resilient enough to be the SOLE source of any information. That's why I expect Apple to make great use file system tags. (Microsoft was going to do something like this in Vista, but it got cut.)
As I've said before, I expect Leopard to have a scalable UI. Again, this almost made it into Tiger, and in early versions (10.4.0 - 10.4.3, IIRC) you could even play around with it if you installed the developer tools (using the Quartz Debug app). It worked decently, but had a lot of rough edges and no decent way to control it. If it makes it into Leopard, I suspect that A) Many of the UI elements (like close boxes, buttons and scroll bars) will be vector-based so they'll never look blocky, and B) An interface for controlling this will be present on every window; e.g., in addition to the resize box in the bottom-right corner of every window, there could be a scale box.
I expect higher-quality visual effects. Exposé is great, but it uses a very ugly scaling method. With the power of Core Image and Core Animation, enabling smooth scaling animations should be easy.
I do NOT expect a Finder that Doesn't Suck. I hope and I dream, but I do not expect...