Header is screwed up when threads are stretched..
 

Anyone know how I can fix this?

When images are to large in a thread it screws up my header. (This also happens on the post reply page if you have the WYSIWYG editor disabled and are using the standard editor instead).

Resize the width of the editor within that style.

When people include images, why not have them as a link or a thumbnail/link rather than the full image?

check out of hacks release section, there are 1 or 2 hacks that will resize large images automatically in posts;)