Panther -> Tiger is more along the lines of Windows NT -> Windows 2000.
Just better
Actually, it's more like XP to Longhorn. That's what Apple and other analysts have been comparing Panther -> Tiger to.
About the iBook/PowerBook - I'm in the mood for some hardcore, indepth essays about the differences!
DESIGN:
iBook- Very well thought out, probably the best plastic-based laptop out there. Doesn't creak as much as, say, a Dell. Ports very well designed.
PowerBook - The best laptop design I have ever seen. With the aluminum enclosure, it feels very solid. It will never creak when you move it, guaranteed. The port placement is also very nice.
SCREEN:
iBook: Two models, 12" and 14". Both are 1024x768 native resolution, both are VERY high-quality, brighter than the PowerBook's for some reason (!), and very clear. You can only mirror though between two displays.
PowerBook: Three models, 12", 15", 17". 12" is 1024x768, the others are widescreen configurations. Possibly the best laptop screens I have ever seen, except for the iBook's, which are strangely brighter for some reason... You can mirror two displays or you can hook it up so that both displays are side by side, displaying various images.
SOUND:
iBook: Great sound from 2 stereo speakers, parallel to the keyboard. Line-out.
PowerBook: Great sound from 3 speakers (2 stereo, 1 center), on the back. Line-out as well as line-in (great for attaching mics for recording, if you're a musician)
BATTERY:
iBook: 6 hours, amazing!
PowerBook: 5 hours (12"), 4.5 hours (15", 17"). Definitely a difference with the iBook and PowerBook.
KEYBOARD:
iBook: Very well thought out layout. However, keys are often not straight and wear away quickly. My only major gripe with the iBook.
PowerBook: Quite possibly the best keyboard I have ever used. Very good layout. Keys are perfectly straight and don't wear away quickly. Typing is a dream with a PowerBook keyboard.
RAM:
iBook: Max of 1.256 GB of PC2100 RAM
PowerBook: Max of 1.256 GB of PC2700 RAM (12"), max of 2GB of PC2700 RAM (15", 17")
PROCESSOR:
iBook: 1.2GHz and 1.33GHz, 133MHz system bus
PowerBook: 1.33GHz to 1.5GHz, 167MHz system bus
OPTICAL DRIVES:
iBook: 12" only combo, 14" combo/SuperDrive
PowerBook: All models either combo or SuperDrive
HARD DRIVE:
iBook: 30GB-60GB
PowerBook: 60GB-80GB
TRACKPAD:
iBook: Great tactile feel, better than the PowerBook trackpad in my opinion, although it starts to wear away rather quickly
PowerBook: OK, but not as good a feel as the iBook's trackpad. Doesn't wear away though.
FIREWIRE:
iBook: FireWire 400 only
PowerBook: FireWire 400 (12"), FireWire 400 and FireWire 800 (15" and 17")
GRAPHICS:
iBook: ATI Radeon 9200 32MB
PowerBook: Nvidia GeForce FX GO 5200 64 MB (12"), ATI Radeon 9700 64MB (or 128MB upgrade)
Sorry, that was long, wasn't it... Hope it helps.