I think you will indeed be waiting a while.
1) Apple will be focusing on the portables first, as they are in the most need of improvement
2) Apple will be focusing on getting rid of the G4 machines first and transitioning those to Intel. There is nothing wrong with the G5s and no immediate need to change them
3) There is a lot of room for the G5 iMac to grow. The current machines are fast, and if Apple threw a 970MP in them, they would last a long time without needing an update
4) on the desktop side of things, Apple is focusing on Conroe and Woodcrest. This is why the PowerMac will not go Intel until 2007, and why the iMac might be in the same boat
I look for an Intel iMac later in 2006. My advice to you is don't hold your breath!