It's a good question. Personally, I tend towards the "write it yourself" camp. That way, you have complete control over your codebase and there are no surprises.
However, I also believe in not re-inventing the wheel
unless you are going to invent a better wheel.
That's why I'm a fan of libraries such as Prototype and jQuery, but a serious denegrator of behemoths such as Spring and
Struts. The former help me get my job done without getting in the way, but the latter just add layer upon layer of complexity that end up making things much more difficult and complex than they need to be.
So I pick and choose which toolkits I employ carefully. I will only use toolkits that help me get my job done quicker without getting in the way, or imposing their own set of restrictions on how I can write my code.
To the subject of this weeks' book promo, I think it's madness to write Ajax calls without the aid of a library such as Prototype or jQuery. Dealing with the browser dependencies and low level status callbacks is a PainInTheKeester™ that these libraries handle nicely.
[ April 09, 2007: Message edited by: Bear Bibeault ]