This is something i suggest everyone should read, just to prepare for what Karazhan is going to throw at us. It's some info of the bosses both lore and gameplay-wise with tactics and so on. Even if you think you already know the encounter to the fullest it's still good to check these out just in case, it never hurts. There's already scattered threads with tactics but i thought it could be nice to gather them all here for people to study. Now do your homework.
1. Attumen the Huntsman:
http://www.wowwiki.com/Attumen_the_Huntsman
2. Moroes:
http://www.wowwiki.com/Moroes
3. Maiden of Virtue:
http://www.wowwiki.com/Maiden_of_Virtue
4. The Curator
http://www.wowwiki.com/The_Curator
5. Terestian Illhoof (Optional)
http://www.wowwiki.com/Terestian_Illhoof
6. Shade of Aran
http://www.wowwiki.com/Shade_of_Aran
7. Netherspite
http://www.wowwiki.com/Netherspite
8. Prince Malchezaar
http://www.wowwiki.com/Prince_Malchezaar
And finally...
9. Nightbane
http://www.wowwiki.com/Nightbane_%28Boss%29
Opera:
http://www.wowwiki.com/Opera_event
And everyones favourite event - Chess.
http://www.wowwiki.com/Chess_event
Please study the Aran encounter especially since both raid groups will be attempting him during the week.