While I can keep trying to persuade you against a left hand nav on a site with this pagerank, you sound pretty dead set on it. As I'm sure you are keeping tabs on analytics, I'd be curious to know how page views change when you implement the new design. It could lend strong weight to arguments. Data always does.
p.s. people read left to right. At least in western countries. Putting up road blocks like a fat nav column before the content they are expecting to see in its place may(will probably) cause usability issues.
Looking at the mock ups and noticed that they had a textured background vs. the plain brown one on beta - looks great!
As far as the nav buttons go, on the forum view page will they have a visual indicator for registered members showing if there's new content (the way the current version shows a light-bulb)? As far as the thread view, will the forum your in be highlighted in some way on the appropriate nav button? Those are a couple of features that I feel enhance useability.
"Instead of Pay It Forward I prefer Plant It Forward" ~Howard Story / "God has cared for these trees, saved them from drought, disease, avalanches, and a thousand tempests and floods. But he cannot save them from fools." ~John Muir
The ideas that you presented that I like are: stuff in the side column. Only with our current approach, it would be on the left and only if there is room.
The idea of a fixed reply button sounds intriguing. Again, something to explore when we get much further along with the beta.
I'm glad I could help as I love permies would like to see it climb on google and reach as many people as possible.
To that end have you thought of doing A/B testing for the new design?
Hey Guys here's another idea I had.
Trying to add more value to the forum category specific pages. This way you can have a "quick read" column that makes it easier to skim for new and return users. The quick read column can be split up into categories. Perhaps: Sticky, Highest Rated, Hottest, Newest... whatever.
Paul what do you think?
P.s. of course this is a mock and not representative of a final aesthetic