Although when it comes to my own collection I am a serious brand snob, I must admit that I caved last Xmas and bought my 3yr old son the McQueen+Mac and Mater M&g@ Bl%ks sets. :-$ I wished for months that they would magically become Lego, but alas, my wish never came true.
The sets themselves are great in design and playability, but the bricks do have an inferior feel - thin and cheap - compared to Duplo. Interestingly, despite the presence of some unique and useful parts, my son has never mixed it with his [extensive] Duplo collection. Influence or Instinct??