One more thing I picked up on.
Your plugin's "resized" images don't have the 2px margin like all other embedded thumbnails do (
at least that's how it is on my board).
The best way to fix this would be to define a unique CSS class (eg. class="imageresizer") in the img tag, rather than just the ID. That way we could style the images anyway we wanted (like fix the 2px margin problem I mentioned above). I'd say this is a critical thing to implement.
Thanks for putting up with my nagging!