It all depends on your needs. I, for being someone who always wants/has the latest and greatest, don't yet want to move to the Intel-based Macs because I find the G4s to still serve my needs. Also, which I've said many times in some of these threads, still use some OS9-native apps that are critical to my work, and therefore need Classic mode.
I eventually down the road, will buy a new Mac so that I can gain performance in such things as Final Cut Studio (which I ordered but never installed yet, waiting for that Intel-based Mac purchase, or a G5 desktop), and what not.
And if you have PowerPC-native applications, those will runs lower on an Intel-based Mac because they run in emulation mode under Rosetta. For some, buying a new Mac does not compute because in order to get optimal performance, you spend more money by having to get the updated versions of software.
Other things to consider are a PowerBook's dedicated graphics card versus the MacBook's integrated graphics card which steals memory from your system. Also, not have a choice over what display you want. MacBooks only have the glossy screen. PowerBooks have the matte. (MacBook Pros have the choice of both. If you want, you can upgrade your PowerBook via third party at TechRestore, to a glossy screen later on).
You can run Motion on a PowerBook G4 (not as fast, but works) whereas on a more powerful (opinion) MacBook, you can't at all. I believe there is a hack, but it wasn't designed to run on a MacBook.
Since I already have a PowerBook, the last one off the line, so the "most powerful," that's as far as I can go with the G4 chip. If I did get an Intel-based Mac, I probably would go, in the interim, for a refurished MacBook from the Apple Store online. For $799, that's a good deal.
Then, there's the plethora of ports on a PowerBook G4 that you won't get on a MacBook. You get FireWire 800, a modem port (in the off chance you find yourself needing one), a PCMCIA slot which can do "anything" currently, S-Video port, gigabit ethernet, and...? A backlit keyboard! If you got the latest and greatest, a high-resolution 1440x960 screen.
Those things alone "beat" a MacBook out of the water. Never mind processor performance.
Again, it's all about preference. Maybe you like silver vs. white. Aluminum vs. plastic. Definitely, using a PowerBook G4, people would consider you a pro since it looks like a MacBook Pro, its equal ("equal") counterpart. A MacBook is like an iBook, el cheapo.
Hey, if you want to argue, and Cornelius might jump on this one, the PowerBook "Pismo" has attributes that would beat a MacBook any day! =)