Yeah, there are G4s now available in tower, all-in-one, and notebook form, but for most needs a G3 will suit you fine. I recently acquired a 4 year old PowerBook G3 233 MHz (nicknamed the "WallStreet") from my dad, who just replaced it with a Titanium PowerBook G4. Of course, his new G4 is beautiful, with its wide aspect screen, CD-RW/DVD player, slim profile, and titanium finish. But that's beside the point.
My computer is very businesslike and utilitarian. It weighs about 8 pounds and it's about 2" thick. A lot larger than either of the new Apple notebooks, but it's still plenty portable, much moreso than any desktop (duh).
The screen is a 14.1" color LCD with a native resolution of 1024x768 pixels. It's very sharp and bright, though it doesn't have the contrast of a tube display. Overall though, the display is excellent and larger than the one on the iBook.
The ports are a bit out of date, with an ADB port instead of the newer USB. I have a SCSI adapter for it but I don't use it much. There are options for adding a FireWire connection if you wish, but I haven't tried any yet.
One of the things I like the most about it is the expandability. Whereas it's difficult to impossible to replace the internal drive in a newer notebook, the WallStreet's expansion bays allow you to add an internal Zip drive, CD-RW drive, DVD drive, or extra battery to replace the standard 20x CD-ROM drive. If I ever wanted extra portability with the extra battery or DVD capability, I'd be able to.
Known issues with this design include the standard power adapter and the hinge for the screen. The original power adapter was recalled by Apple and the replacement was the more portable yo-yo power adapter. The hinges are known to get loose over time, and a couple of people have suggested going to pbparts.com to get replacement steel hinges. Luckily, mine hasn't gotten loose yet.
As far as speed is concerned, it's plenty fast enough to run EV Nova and Unreal Tournament, and surfing the internet is faster than on a slower computer with an equal connection speed. Unless you're doing high end games, Photoshop work, or heavy multimedia applications, it should be fine for most things (e-mail, internet access, word processing, smaller games, etc).
Keep in mind that a PowerBook will cost more than a desktop of equal capability, and it'll be less expandable. My computer would probably sell on eBay for around $500-$600, but a beige G3/233 with keyboard, monitor and mouse would probably sell for under $450. A desktop allows you to add larger monitors or multiple monitors, offers many PCI slots for upgrades, and lets you install larger hard drives, more RAM, and better graphics cards and CPU upgrades than a PowerBook will. Also remember that if you use the portability a lot, you'll end up running the risk of theft. It's just as easy for a theif to pick up your 'book as it is for you to.
Overall, this is an excellent computer. Sure, it doesn't hold a candle to a G4, and I would really like it more if it had FireWire ports, but it's still very useful. I end up using the portability more often than I expected. Taking practicality, fun, and portability into account, I'd have to rate this notebook an 8.5, docking points mainly for the lack of FireWire/USB and for the size and weight. I've seen the new iBooks and they're just miniscule compared to this beast. So my advice would be that if you want a fairly fast PowerBook and don't mind it being a little bit dated and heavy, this would be an excellent choice.
A clarification for those of you who may be confused or wanting to buy a G3 PowerBook: The PowerBook I just reviewed was named the PowerBook G3 Series II, which is easy to confuse with the earlier PowerBook G3 and PowerBook G3 Series models, and the later PowerBook models. Apple's naming system is very confusing, so generally this line (which included a 233, 266 and 300 MHz model, all of which had 14.1" screens) is referred to as the WallStreet or WallStreet 2. An earlier 233 MHz version nicknamed the MainStreet should be avioded because it lacked a cache, making it slower than the non-G3 3400. The MainStreet had a 12.1" screen, while the other models in the line (a 266 and a 292 MHz) had 13.3" and 14.1" screens, respectively. Later, to replace the WallStreet, the 333 and 400 MHz "Lombard" versions were introduced. They were slimmer, lighter, and had DVD drives instead of CD drives, as well as a larger hard drive. They also had a distincive translucent bronze keyboard and trackpad button. Lombards had USB ports but no FireWire. Finally, the 400 MHz and 500 MHz "Pismo" PowerBooks replaced the Lombards and added two FireWire ports in the process. Also there was an upgraded graphics card and full support for OS X. So there you have it. If you want a good one, look for a WallStreet, Lombard, or Pismo, or go to lowendmac.com and read up on the specs for each one.