Looks like after doing a bit of research, I need to modify my last statement.
The latest batch of Core2Duo processors actually out-perform the G5 processors when running PPC-specific applications, despite having to run them on the emulation layer Rosetta. So even though the latest processors are emulating older programs, they are still faster. This is quite an achievement as emulation generally saps a good deal of performance out of an application.
Some examples of PPC specific apps are Office 2004 and Photoshop CS2. While the performance within these apps is equal to or greater than that of the PPC processors they were designed for, the loading time is where you notice the hit as it takes a bit longer to startup an emulated program. Though once you're in, you won't be able to tell the difference.
Fortunately, Microsoft will be releasing a Universal version of Office later this year and I believe Adobe has already released its Universal Photoshop CS3. In fact, most of the apps I use are Universal and those that aren't, the author/publisher has a Universal version planned.