My father and sister both started Mistborn before me, and both stopped around midway through the first one. I almost did too, but I don't leave books unfinished unless they're really horribad, and came to love it.
Maybe I'll bait them back into Sandersons's works with WoK, since I thought it a really enjoyable read, despite it's length.
I'll definitely buy my cousin the Mistborn books, since I know she loves these sorts of books. Maybe WoK too, but it's so long and she's pretty young... But who knows, she also plowed through ASoIaF with no problems.