I've just launched a new version of our site which uses version 4.1.4 of InstantForum. I've had to modify the source a fair bit to get it to behave how I like, and still have changes to make, but you can see it at:https://londonbikers.com/forums/
I've moved the file attachments from the DB to the file-system to stop my database getting out of control, and have modified the thread pages so they render attachment images inline with the post, and if they're bigger than a set size, dynamically resizes them down to an acceptable size.
I also had to integrate it with my own UMS which was more difficult than with prior versions, so I'm still looking for some answers on things, but there doesn't seem to be much support available on these forums.
I created a new skin as well :)