Pros:
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1) Smallest Mac around.
2) Fast enough. But then, so are most of the Mac portables these days.
3) Unlike the iBooks (unless you flash them), they support an external monitor as an extension of the desktop area, rather than a mirror. Also, you can have a higher resolution on the external monitor.
4) Bluetooth and wireless built in by default.
5) Beautiful Aluminum chassis.
Cons
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1) No gigabit ethernet. Sure, not everyone uses them, but these are available on the 15" and 17" and it would be nice to have them on the 12" as well.
2) Firewire 400 instead of 800. I'm not too bothered by this since I don't have any firewire devices. It might be an issue to others though.
3) No PCMCIA slot. Again, it doesn't bother me unless I run Linux on it. But it shouldn't be too big an issue.
4) The chassis is made of aluminum. This means it gets quite hot. Also, if you live in a dry climate and have static electricity build up, this could give you mild electric shocks unless you ground yourself before touching your machine
. This affects all Powerbooks though.
5) Battery life isn't as good as the iBooks. But then this also affects all powerbooks.