Thanks for the nice list n0ah! Lots for me to check out there, as most of those should be working.
Just a note, we inherited the original forum code from the JooBB project, and have been gradually improving it, and fixing bugs as well as adding features, so there are still quite a few things we haven't even realized are wrong with it yet. Which is why I appreciate you taking the time to let us know.
But you will be happy to know that in the latest release (out yesterday) was:
* a fix for private boards appearing in the recent posts area
* attachments and image embedding fixed
The separated CSS files were because different elements of the design were separated, but we are going to be fixing that up in a later release, as well as the language files being separated.
I will check out deleting, the more than one page thread error, and public members posting in private boards and if I can sort it out quickly I will release a quick patch for them.
Yes there is no PM system, and at this point no plans for one as there are plenty of good alternatives out there (plus we don't have the resources right now for another major project) but if you can suggest some good ones for J1.5 then we can also look at integrating them into NB.