I have just started using Burn Folders under Mac OS X 10.4. I had previously dismissed them as similar in concept to the old Mac OS 9 style burn folders -- which basically just created a hidden disk image, then burned the disk image to media. IMHO, this was a long way of doing a pretty simple thing. But after reading some comments about Burn Folders and how they used aliases, I thought I would give it a try. So this weekend I started experimenting with Burn Folders, and found them to be quite useful.
Except for one little thing I discovered quite by accident. I had created a Burn Folder and dropped a few other directories into the Burn Folder, which in turn had a few directories inside them. I realized just before I decide to burn the Burn Folder that I really didn't want to burn a few of these sub-directories. So I proceeded to go into the directories in the Burn Folder and delete the items -- thinking I was just deleting aliases to the items (as their parents are). Luckily, I decided to investigate before emptying the trash. Turns out that only the top level directories you drag into the Burn Folder are actually aliases. If you dig into those and start tinkering, you are actually modifying the original files on disk.
Now if you think about it, this is probably the way it should be, and it is the way the rest of the system works with regard to aliases. I was just a little stunned that I was able to so easily delete data without a warning or anything. Maybe Apple should somehow add a trigger mechanism to the Burn Folders that alerts the user that any modifications you make to items inside the main aliases is actually modifying the real data files/directories.
[robg adds: The behavior of Burn Folders can be a bit disconcerting, but it's definitely normal practice for folder aliases in general: once you double-click an alias folder, you switch into the actual directory (since the alias itself is just a pointer to that folder). Relative to Burn Folders, Apple tries to provide some visual guidance to help. When you're in the top-level of a Burn Folder, you'll see this header in the window (in list, icon, or column-view mode):

Mac OS X Hints
http://hints.macworld.com/article.php?story=20050912173100775