I've only owned two so far. My first one was a 12" PowerBook G4 1 GHz, which is now in the possession of my girl friend.
My second one was a 17" PowerBook G4 1.67 GHz, which is no longer working properly (it no longer runs on battery - and I've got two functioning batteries for it - and it switches off after a few minutes when running on AC power). It's a shame, because I really, really liked this machine, but I'll put it on eBay Germany tonight. Maybe some lucky guy will be able to fix it, I personally no longer care and currently have a load of other things to take care of and spend money on.
At the moment, I strongly doubt that I will buy a third Apple notebook anytime soon. I will get a new notebook (probably a Dell XPS) from my new employer which I can also use privately, so I don't have a need for another mobile machine. I still have my Mac Pro for everything else.
On a general note, I think that the PowerBooks were gorgeously looking machines, but I must say that they did not necessarily convince me quality-wise. They were not very robust for mobile computers, but were rather the type of beautiful thing that should not leave the desk because it's too fragile for real-world use. A friend of mine owns a first generation 15" MacBook Pro, and it leaves the same impression on me as the PowerBooks. My old Gericom X5 Force was "a real pig" in comparison: That baby was meant to be carried around and used under heavy conditions. And even my Toshiba Satellite before that felt more outdoor-friendly than the PowerBooks.
Also, the current Apple notebooks are plain and simple way too expensive. I'm always willing to pay a premium for a nice design, but a high-end Dell Precision notebook is a much better value and comes with better service than a 17" MacBook Pro and, frankly speaking, the XPS series already offers more than one usually needs at less than half the price of a MacBook Pro, but with an equivalent performance.