I use simple skin for one main reason: fonts are too small in other skins.
Other things I don't like in general:
1) Both modern skins are with colors too vivid, it is sometimes distracting, especially while looking at photo attachments. (Would we frame photographs using bright red or bright green frames or window mats? Probably not.)
2) All skins use a lot of space on headers, footers, space between posts, and so on. Short posts get entirely eaten up by "white space" and other elements of secondary importance.
3) Perhaps placement or captions on reply buttons could be improved. I often see a lot of people reply to the last post, not the the intended message. That makes following discussions a bit hard sometimes.
4) Threaded mode sometimes does not work in any skin: sometimes the navigator frame is simply empty, sometimes clicking on "More replies below current depth..." simply resets the threaded view to the first post so additional posts are inaccessible, and switching to Linear Mode is necessary.
5) Speaking of threaded mode: can thread navigator go after the message, similar to DPReview?
6) Finally, I would prefer a darker skin, with more efficient use of space, highlight on message body, and limited width. Here is the example of a type I like on Onexposure - it is very compact, with nice headers:
Onexposure - 1x.com - Photography forum - About forum "Photography"
Adam: is there is any manual or guidelines for making skins for this forum engine? I would like to try creating one if you don't mind.