One thing I won't miss from the Tibook is the painted border around the corners that chips from contact with my watch band. All in all, the Aluminum seems to be a better material for the case than the titanium Apple was using, despite the reduction in cachet. Everybody seems to think that titanium it like Mithril, some sort of magical metal. Truth is, it's no better than aluminum for many applications that don't require high structural strength.
The feature that I loved from most of the G3 Powerbooks (and some of the Vaios) was the ability to remove the CD drive and replace it with an extra battery. I realize that the engineering demands of the smaller form factors make this more difficult, but I really liked having 7-8 solid hours of battery life when I carried my laptop from conference room to conference room, or on a flight from Miami to Cape Town, South Africa. I rarely use the CD/DVD drive anyway, so I'd love to see that feature return in my Fantasyland Powerbook.
I love the return of the small form factor. I really loved the Powerbook Duo 2300c, which is a well-beloved machine in Powerbook-land. It had almost no ports or expansion, which is one area that this compact Powerbook shines. True, it has no PC Card/Cardbus slot, but has built-in what you'd probably need one for. I use my PC Card slot to read Smartmedia cards from my camera, but I can get by using USB for that. Everyone can make a short list of the connectors that this Powerbook could have but doesn't: USB 2.0 (probably because of Apple politics and weak demand from Apple users), DVI (too expensive considering that few Powerbook owners use it, perhaps?), Firewire 800 (too new), PCMCIA/Cardbus (no space). Personally, I'd pick a handle over any of those ports. My computing experience is not diminished for their absence. Truth is, with USB and Firewire, you can plug almost anything into it that you might need to.
I really like the latest Apple power adapters. I love the flip-out plugs with the optional extended cord. I love the flip-out wraps for the cord. I really love the light-up plug that tells you whether your Powerbook is charging or not. It's small, self-contained, and feature-rich but simple. It's represents the best of Apple engineering.
I'm so excited to use the built-in Bluetooth I can't stand it, but I don't have anything to use it with. Bluetooth phones are pretty rare in the US, though I really wish I had one now, and other bluetooth accessories are rare everywhere. Of course, before the iMac came out, USB stuff was rare. Maybe Apple can give Bluetooth the boost it needs too.
I'll second what everyone else says and say that the keyboard is great. I kind of wished it were dark-colored like my Tibook, but that might just be prejudice that will wear off with familiarity. I am deeply disappointed that the 12" Powerbook does not have the backlit keys like its 17" cousin. In fact, I bought it after Steve Jobs failed to mention that the 12" Powerbook did not have this feature when he announced it. Nevertheless, the keyboard has a great feel and a good size. It still has the silly "fn" key in the lower left hand corner where the "ctrl" key should be, but I'm already used to that. Aesthetically, I think the keyboard is a bit ugly, both in color and shape. We Mac users are always whining about aesthetics, aren't we? I didn't want to disappoint anyone by not having an opinion on this subject.