UPDATE April 6, 2006.
Thanks to all you who have given me suggestions on what to add to the list. I include them in this post.
What should I include in this chaper?
Here is my list of things I should write about (inspired by Think Big:
Blogs – with comments enabled
Wikis – with discussion tabs
RSS
IM/Chat
Social tagging/folksonomies – del.icio.us, cite.u.like
Social networks – LibraryThing, Flickr, Orkut, friendster, myspace, spray,
Podcasting/videocasting/vlogging/video podcasting
Massive Multiplayer Online Games (MMPOG), Network worlds and games – World of Warcraft, Anarchy Online, Halo, runescape
Mashups
I'm a norwegian librarian.
Librarian 1.5 
Don’t forget videocasting/vlogging/video podcasting.
And don’t forget runescape in your worlds/games section.
And – cool idea on the online versio of a book – keep it up!
And blogs with comments enabled! And wikis with discussion tabs!
Thomas — this is great stuff!
Two of the categories I’d add to my “Starter List” are video (e.g. YouTube) and MMPOG. Keep up the good work!