I'm personally a fan of collapsable threads. If you go back to Hubski's inception, it was cloned from HN, which doesn't collapse. Probably would never be able to tell as mk has transformed the site so completely, but certain absent features are probably legacy omissions. At this stage, I think that collapsing comments while nice, aren't a top priority. Hubski traffic has been increasing steadily, and as it continues to, there will come a time at which average comment volume reaches a critical mass and the site will probably need a feature like that. But HN has much more traffic than Hubski at the moment, and they get by without it...although I find myself wishing they had that feature quite often. I guess I'd say that Hubski should implement it well before it reaches HN's volume.