I realise this is probably a long shot, but is there a way you can limit the size of images that people link using BBCode, and if it is larger, scale it down to a pre-defined width?
I'm building my forum with a fixed width, so you can imagine things start looking ugly if people link images that a wider than the forum itself.
There was a discussion about image width a little while ago. I've got a feeling it was mooted as being in the next revision using the same code from filebrowser. Have a search and see what turns up.
I did a search and couldn't find any mention of it. oh well. if it's headed for the next revision though, well I guess I'll be sorted soon enough then!
Oh and nav: that doesn't resize, that just adds scrollbars to that particular post.. and only in Firefox (not too sure of any other browsers that support it.. not IE though).