It seems to scale to medium size OK (several thousand lurkers, ~100 regular posters and a steady stream of drive-bys), though I observe even a medium sized subreddit doesn't feel all that different than a Usenet forum of the same size. Voting may let the community get a little larger than just a threaded conversation, especially because it can distribute spam filtering, but I'm not sure it's that meaningfully different in the end.

I'm also not convinced it's terribly detrimental. Most of the accusations against vote systems are true of threaded forums in general. Group think develops, regardless. People can be hounded out of a community, regardless, for the same set of reasons. It seems to me the real key is the use of a threading system in the first place, rather than the votes attached to the threads.

It may be fair to say that threaded voting enables the largest communities I know about. At the scale they break down, I don't know anything that works. I've never seen a mechanism for having a tightly-knit single community of larger size without being what most of us would consider a community fail.

By contrast, threaded vs. flat is a vital change.