Interesting question.
I have a powerbook and love it. I have never dropped it - but I am not sure how I would fare if I did. However - I have watch my friend accidentally drop their iBook TWICE from about 2 1/2 to 3 feet up. The iBook survived the two drops. I asked somebody at apple and they said that the iBook was built for schools and for ruggedness. I believe it.

You can go wrong with either one of them.
I have a 15 inch PB.

One advantage of the PB is that it has two graphics cards built in. The iBook has one. In both cases you can add a monitor. The PB allows separate sessions on the external monitor and PB display. The iBook allows you to mirror the PB display on the external monitor.

I'd suggest a 15" Powerbook. A train would probably render the 17" too bulky, and for development you would want more screen than the 12" offers.

The iBook may be fast enough for Java development these days, but there are things that the iBook can't do without unsupported firmware hacks, like spanning multiple monitors. The Powerbook, on the other hand, will also make a pretty good desktop replacement.

Charles, I presume you meant to say "You can't go wrong with either one of them."

How much memory do you recommend for Java development?

What does a PowerBook set you back these days?

I owned an older 667MHz Titanium PowerBook, and just recently (2 months ago) picked up a new 1.5GHz one. For software development, I recommend going with the best you can afford. The difference between a new 1.5GHz machine with a gigabyte of RAM, and a used 800MHz PowerBook will be significant. I suspect even the 1.0GHz (iBook) -> 1.5GHz change to be noticable.

Buy the best, love it severely for a few years.

I've had both a 12" iBook and a 15" PowerBook. After using both, I prefer the iBook.

The newest iBooks are very similar to the PowerBook lines. Very similar processing power and same RAM limitations (in the 12" model). The most compelling feature (for my use) that the PowerBook offers out of the box is monitor spanning, though the iBook can be easily configured to support this.

Sure, the 12" screen is smaller and these laptops have less RAM than their larger brethren. I've always valued both screen real estate and RAM -- my desktop systems run at no less than 1600x1200 on 21" monitors, with at least 1.5GB RAM. However, I've found that the smaller 12" system is by far more portable and easier to use on the road than the 15".

I had no problem carrying the 12" everywhere I went. With the 15", I only brought it along when I had to. I never felt constrained by the small screen (which, frankly, surprised me), and I never had a problem with the RAM limitations (despite doing some fairly heavy development work.)

Thanks for all the feedback. I've pretty well decided to get an iBook with an extra 512MB of RAM as well as a wireless card. It is likely to set me back a little over A$2,000.