I'm somewhat nervous about system requirements. I read this whole thread hoping to find some information on that, because with the partnership with Dell on the WoW computers and the new Vista, I'm worried I won't be able to actually play on the expansion. I am definitely not going to buy a whole new computer just to do it, though. So basically, I'm trying very hard not to get excited about it, since I might not be able to play it anyway. Has there been any information about that yet?
As for Death Knights... The only thing I worry about is that with all the other classes, you have a lot of time to figure out how your class works, starting with extremely easy quests in your home area. Starting out suddenly at level 50 with a whole level 50 library of spells and abilities, *especially* with a new system (runes)... That's going to be a little complicated to learn. I still have troubles remembering when/how to use some of the spells I got ages ago (Psychic Scream and Fade), and I'm only level 34. So, I definitely don't think that Death Knights are going to replace Paladins. Plus, unless the character slot thing becomes nearly infinite (or at least, perhaps, an empty slot next to each original character that could become a hero class), people are not going to make all their characters into Death Knights in order to learn how they work. So, while there may be a lot of them right at first, there will probably only be one Death Knight per player per server.
Finally, as to the semantic issue of "no one said they are going to be tanks" and "Blizzard said they will have tanking abilities" -- I think these two things go together quite well. They will likely be *able* to tank, but that does not mean they will all *be* tanks, any more than all shamans being healers, even though they have healing abilities.