Individual collapsible comments

I can't be the only person to suggest this, but I couldn't find any similar posts in drupal.org.

Inspired by the collapsible fieldsets implemented in D5 to make Forms (a lot) easier to navigate, I thought it might be a good idea to apply the same functionality to lists of comments.

Currently, we can select the overall collapsed/expanded and threaded/flat formatting of a comment 'block'. Would it be very problematic to replace the collapsed/expanded bit so that individual comments could be collapsed & expanded in context using AJAX ...?

Zach points to some really nice jquery tricks in a thread starting at http://drupal.org/node/118343#comment-224508.