I switched from UBB.classic, to vbulletin (short lived) to UBB.threads.. and each upgrade people bitched and moaned.. this feature was different, or this one was missing.. etc etc... I had to sift through hatemail for about 3 weeks.. then suddenly, everyone shut up, and the only comments I heard were "This site is the fastest forum I visit!" and "It looks to clean, no useles graphics hogging space" and such...
Like Josh said.. it is completely different, and isn't meant to simply be an upgrade for classic. It has most of the features, but at the same time it has extra features, completely different look, and is much more powerful overall. Your users won't acknowledge this immediately, but over time they really appreciate it.
Most users now praise my site saying it is much easier on dialup connections, and they enjoy a lot of the small features that aren't really advertised. Also remember, threads is very new when compared to these other products, and with each version it just gets better and better
