I've found what I think to be a pretty serious bug with the way file renames are handled in Vista.  One of the cool new features in Vista is that you can select a bunch of files and rename them together.  This creates a sequence of files where the filenames are the same, but each has a different number at the end - e.g. "Hawaii.jpg", "Hawaii (2).jpg", "Hawaii (3).jpg".

It's obvious why this feautre is useful, but here's the problem: if you undo the rename (ctrl+z), all the files go back to their origianal filenames - as you'd expect; however, if you then redo the rename (ctrl+y), all of your files disappear (with the exception of the first file in the sequence).  Now when I say disappear, I mean it.  If you try to undo the redo, you get a message saying that Windows could not find the items to rename.  Also the missing files don't show up anywhere, not even the Recycle Bin.

Go ahead and test this out, but make sure to have a copy of files elsewhere first.  I have tried it with many different types of files, and with different file types at the same time, and the results have always been reproduced.  If you are trying this and ctrl+z doesn't work, you might want to try pressing the "Alt" key to get the classic menu up, and select it from there.