In the past few years, the boards have created both popular threads, and also threads that have ended up being somewhat notable, for whatever reason.
The plan of the archives is to store these threads permanently,
however boards will only get this when there has been enough significant
threads that mark keeping hold of them. Of recent, boards with threads inactive for more than 18 months have been archived, simply to help clear out stale threads, as well as threads which have reached the post limit. partially also because Kareha gets sluggish after several thousand threads. There is currently no active schedule for archives.
In January of 2007, the front page was briefly changed to look something like a very bad web 2.0 page.
Since 2005, the Internet Archive has been spidering, and collating its own archive of Channel4.
The old version of the sidebar from ~2006 can be seen here. The current sidebar corresponds to the main site boardlist until early 2021, when some boards were merged/retired.