The result, at least before the final version of Leopard came out, was a shelf-like Dock that looked anything but a shelf when positioned on the right or left. Apple's ungainly solution in the shipping version: Transform the Dock when it's placed vertically.
Instead of a sideways glass shelf, you get a dark, sleek, translucent strip ringed in white -- basically, a modernized version of the old Tiger "Scotch tape" look. Some people don't like it, some do. But it's a little weird to have such a major part of the user interface change its look based on where it's located. It feels too much like an afterthought.
(If you really don't like the shelf-like Dock, there are Terminal commands and scripts available to get it to appear as a strip even when it's at the bottom.)
The stacks that reveal the contents of a folder in the Dock are a nice idea, but some of their behavior is annoying. First, if the Dock is on the bottom of the screen (where a lot of people tend to keep it), a stack will display as a curving column of icons or as a rectangular grid, depending on how many items are in the folder.
For folders where the number of items changes regularly (such as Downloads), you never know which display you're going to get. Furthermore, stacks displayed as columns sort items alphabetically beginning at the bottom of the stack, while stacks displaying as a grid sort items alphabetically beginning at the top left. Between that and the changing shape, you can rarely find what you're looking for immediately.
Another miss with stacks is the fact that there's no easy way to navigate within them. In previous Mac OS X releases, folders placed in the Dock functioned as pop-up hierarchical menus for navigating their contents. It would be nice to get this functionality back.
When you first launch Mail in Leopard, it imports and converts your e-mail database and all your mailboxes. But some people who went through this process then found that rather than seeing all their mail in all their in-boxes just by clicking on the main Inbox header, they had to view each Inbox's mail separately, by clicking on each mailbox individually. Needless to say, that's a serious inconvenience.
Active Directory support doesn't seem to be completely reliable so far. Many users are reporting problems with Active Directory binding under Leopard. Binding to a domain and logging in both seem to be slower across the board for most users, and a number of people have reported other problems beyond just sluggishness. Given that for many people and organizations Active Directory support is a priority, this is a major miss.
Admittedly, Cover Flow in Finder windows is cool. It allows you to visually scan files and folders the same way you flip through songs and albums in iTunes or on the iPhone.
Here's the annoyance, though: You open a Finder window in Cover Flow mode, then drag the lower-right corner of the window down to see more files. Oops! Watch instead as the Cover Flow icons grow to gargantuan size while the list of files you're actually trying to expand remains the same size.