some remarks (General)
I wanted to make some remarks on several things.
first of all, i think the ajax preview-featur isn't really necessary.
either i want to view a certain posting or i don't. in both ways, i have to click once. so, there is no simplification. perhaps you should make it optional.
secondly, i think it would be better to not only take over the subject of a posting when answering it, but to add "re:" to it.
furthermore, i don't understand why the username of the author of a posting is saved into the entry-table. what if i wanted to change a certain username later?
last but not least, i don't get the point what actually is the difference between board-view and viewing the whole thread in thread-mode.