Originaly the moniker "Power" added to the front of "Mac" was used to denote the switch to PowerPC processors rather than 68k processors. Now that Apple is moving from PowerPC to x86, I can't help but wonder what will happen to the PowerMac and PowerBook lines, since in a sense they are clearly no longer "Power" computers. Interestingly enough, at the same time Apple already has a nice line of "X" products, e.g., Xserve, Xraid, Xsan, Xcode, etc. It seems only natural that when the new x86 based Macs start coming out that the "Power" line would be renamed to the "X" line, making them the Xmac and Xbook. This would create a very clear distinction between the low end consumer "i" line (i.e., iMac and iBook) and the high end pro "X" line.
Now, I'm not generally one to pontificate about future events, and I think the likelyhood of this happening is rather slim. I'm not even sure what I think of the whole idea, but it just seems plausible.