One of the bigger annoyances many folks have complained about with Leopard is the loss of hierarchical file browsing of folders in the Dock. Of course in Leopard you get Stacks, with all their fancy fanning and gridding, but you lose the ability to right-click a folder and dig into the sub-folders. As a solution/work-around many folks have suggested the venerable Dock replacement Drag Thing. But it has a lot more features and at $29 is a bit of overkill just to get that one feature back. So instead, you might have a look at the free Hierarchy from Charles O'Rourke.
Hierarchy is a dead simple application. All it does is create a little floating HUD-style vertical palette onto which you can drop your folders. Clicking on those folders opens them in the Finder, but better yet right-click generates the old Tiger-style hierarchical menus. Of course, this adds another (potentially annoying) palette window to your desktop, but it does a good job at its small task.
Hierarchy is a free download from Charles O'Rourke.