Jon,
The Annexe looks good.

Paging versus scrolling isn't a showstopper for me and my preference is a mild one. Without getting too "touchy feely" a thread that one pages through "feels" different from one that one scrolls through. The posts in the former "feel" a little less connected than those in the latter.

"members only" posting is also not a showstopper but my preference for the open system of Mudcat is much stronger. However, I participate in both types.

The BBC site is a good example of the downside of forum splitting. Where there are too many categories and they have not been created in any systematic or consistent way it can be very difficult to find what you are interested in. I think I prefer a few "big" categories rather than a bunch of small ones, e.g., "Music" and "Not Music" for Mudcat.

Ironmule,
I too like the idea of being able to edit posted posts.