I have been very busy lately, but I have been working on the collapsing archives update for awhile. I have incorporated new features from collapsing categories into it, while trying to keep all the old features. One thing I have learned is that it is difficult to write code with many options, especially when some of them interact.
Since I released the collapsing categories update a bit prematurely, I have dubbed this one 0.9.alpha, and I have not given it a stable tag yet. So you will not see that it needs updating when you look at your plugins. I do think it is fairly stable, and would be very appreciative if a few people tried it out.
You can download it from the official wordpress plugin repository.