I was chatting with occasional Hints editor Kirk McElhearn this morning, trying to figure out a Word 2008 image placement issue related to using the arrow keys to position the image. If you use the arrow keys alone, the image moves in large increments (10 pixels at a time, maybe?). For fine image movement control, Word 2008's help says this:

To move an object up, down, or sideways in small increments, click the object, hold down OPTION, and then press an arrow key.

However, this didn't seem to work -- holding Option and pressing any arrow key resulted in no movement at all. Yet Kirk had a document he was editing in Word 2008 whose images would move by fine amounts with Option and the arrow keys. When I tried on my local Mac, though, I had no such luck. After some digging on Microsoft's Word Forum, I found a thread (for a related question) that provided the answer. User CyberTaz wrote:

Rather it is caused by the new [different] graphics engine in 2008. Whether it's a bug or intended to be that way I'm not sure, but it is definitely different behavior than what was in 2004. In fact, if you are working with a .doc file, you retain the 2004 behavior because the program still invokes the older graphics engine.

The document Kirk was editing had been saved in Word 2004 format, which is why the placement feature was working for him. If you need fine image placement control in a Word 2008 docx document, however, you'll have to use the mouse (and the Command key, to override the default grid). I assume, but haven't tested the theory, that the same is true for images in PowerPoint 2008's new and old file formats.

Hopefully this is just a bug that can be patched in a future update (it's not fixed as of the Word 2008 12.1.1 update), as it's annoying not being able to use Option and the arrow keys to finely position placed graphics.