I've been thinking about picking up a kindle for quite some time now, cant really justify picking up an ipad, but I've only really ever seen it advertised or demonstrated showing ALL text. I'd be picking one up for saving my "Technical" books on. So it would need to be able to display the general kind of diagrams you see in Graphics, Maths and science books. How well do they do this?

At the moment, most of my books are pdf, but from what I gather you can convert these to a compatible format for the kindle.

And then the final factor is the 6" screen. Too small?

i think its pretty cool if you read a lot. the screen should be big enough

The kindle is fantastic for novels. Based on what I've read, it's not so good for larger format books, especially those with graphics. The Kindle DX on the other hand is supposed to handle those types of books very well, but I have no experience with them.

Edit: Here is a review which shows the Kindle DX vs the iPad on a document with graphs and images. I'd say the Kindle DX does a very good job on that type of document.

Kindle DX Review

The kindles are great. The thing that tstrimp's image doesn't really do justice with is how it actually feels in different lighting conditions.
Kindle's electronic paper looks like paper. It isn't back-lit, and it doesn't have a glossy finish. You don't have to deal with glare, or other too-bright conditions that wash out a tablet. You don't get blinded by it at night, cause it doesn't emit light. If you could read a regular book there, you could probably be reading your kindle.

i just got the kindle and i have put several pdf' onto it. The diagrams come out fine but i've heard some books have issues. I dont think the occasional dodgy diagram is much of a deal breaker, the text is more important.

In my opinion the UI of the menus is a bit clunky but it doesnt interfere when reading.

Either way it beats the hell out of big hardback textbooks, you cant handle that on public transport standing up.