We got our hands on FastMac's replacement AC adapter for Apple iBooks and PowerBooks and can say that they're pretty much as good as the standard. Ignoring the dubious benefit of being able to be kicked and run over by an SUV (which you can see after the jump), they actually work quite well.
Using it on a G4 iBook (whose battery was replaced last year in that recall), it took about three hours for it to charge from empty to full. That's pretty much the same as the official charger.
The only difference is that the official ones from Apple cost $79, and the one from FastMac costs $35. And there's no orange/green glowing ring where the charger connects to indicate whether it's still charging or already full. But if you can live with the fact that the chargers look a bit more "PC" than "Apple," these are the way to go.
Product Page [Fastmac]