If you can't afford to repair or replace the iBook after the warranty is up, you might want to consider getting AppleCare. Remember you can buy it (and register it) anytime before the warranty expires.
Some people get it no matter what, some people get it if their systems had a problem during the warranty period and some never get it.
From my point of view, a laptop can get a lot on abuse that doesn't show as user damager and therefore would be covered under AppleCare.
If you're getting a base $999 iBook, then AppleCare probably isn't as worth it as if you configured it to the maximum configuration of around $2100 (US) since the AppleCare costs the same for either.
Paying $150 for AppleCare on a base MacMini also seems a bit ridiculous.
On the other side of the coin, buying a top end fairly loaded PowerMac (with a 30" screen) will cost from $7000 to $10000 or so and for that the $250 PowerMac AppleCare is but a drop in the bucket and well worth it.