i saw that at Blizzcon or w/e that u could trade ur pally for a death knight at lvl 80 after a big quest... and if thats true idk if i should do it. i have a lvl 70 holy pally atm and when i get to 80 idk if i should give him up becuase i dont know what a death knight will even be like and i like my holy pally. SO if i do trade my pally in and i dont like the death knight im screwed but if i dont trade my pally in ill never know what a death knight.... so what would u guys do if you were me?

DO IT!... or you could wait until other people go for it first so it won't be as big of a mystery about what it is like to be one. 

you do not trade any class in you keep your char you can get it as any class no trade in, please pay attention to the known facts. 

that's dumb you wont have to switch your character out for another one. It will be like another default you can choose to start at level 1.
And if it is then wait for other people to get the dark knight and check out what there like and soon thottbot will even have a database for the dark knights.

they start out at like lvl 55+ and u dont have to switch anything in for em as long as u got a lvl 55+ char

and btw at least spell it right its death knight not dark knight

U know when WOTLK comes out the BGs are gonna be hard coz everyone will be a death knight and it'll be fun fun fun! *ahem*