I have the old iBook 500 with 384mb ram. It had only a 66mhz bus. Its still snappy enough to use as an everyday web-surfing-mail-scanning-chat-hopping machine and puts in a decent performance when it comes to office and basic design/web stuff. Don't write off the new iBooks until you've tried one. Sure, it won't compare to a G5, nor will it keep up with the powerbooks on graphics and multimedia processing, but it is still a delightful little machine.
Max out the RAM if you can, and whack in an Airport card, and you've got a computer that will give you years of easy use as your everyday laptop.
If in doubt, try one out. Pop into your nearest Apple store (if you're lucky enough to live within a couple of hours of one) and put it through its paces with the sort of tasks you want to do. Its not too shabby.