1) a dictionary can be used whenever you want, to look up a specific word in mind only (you cannot leaf through it for ideas)
2) When it is your turn, before playing your letters, you may swap a letter in your hand, for a letter on the board. This can be done as much as you like, but only one letter at a time, and each letter must make a new, valid word. No points are scored when swapping.
The result is that turns can take 10 minutes or more, but bingos are very common and individual scores get into 5-600 points often. There is much more skill and very little luck- as you are not limited by the letters you draw- rather, you can use just about any letter that's on the board, if you can get it! Likewise, if you draw the X you are not "lucky" because the X will likely get used again and again over the course of the game by multiple players.
I'm not sure how common this variation is, but I like it, and it's well-suited for serious players.