Actually, the title is misleading. I liked almost everything in the episode, except the fact that it was an episode. (My favorite moment: Rainbow Dash out-nerding Twilight Sparkle in a Daring Do fan argument. Pure gold!) It was, for me at least, much less than the sum of its parts.
I find that an Equestria, where there is room for a long-running series of books about a fictional adventurer Daring Do, fighting fictional villains over fictional artifacts in fictional locations, feels more fully realized than an Equestria where Daring Do is real on the same level as the Mane Six.
I also find that having Rainbow Dash fall in love with a series of books, to the point of totally geeking out over them and writing fanfiction of them ('cause you all know she totally does that) is both more fun, and adds more breadth to her character, than having Rainbow Dash be a huge fan of the real-life adventurer Daring Do. We already have Dash being a fan of the very real Wonderbolts; this does not add anything to her character, and arguably takes away from the moral of Read It and Weep, one of the best episodes of S2.
Finally, I find it hurts my suspension of disbelief that Daring Do and everything about her can be real, and that this comes as a complete surprise to Twilight Sparkle. She is a Daring Do fan and an obsessive researcher of arcane and odd lore, with the run of Canterlot's archives and a personal relationship with the Princesses of Equestria even before her ascension. I can't believe that her favorite books are real, and that she had no idea of it.
Thus, I find myself in the weird situation of having quite enjoyed the episode, but also wishing that the show will completely ignore everything about it. As far as my personal take of Equestria is concerned, Daring Don't is going to occupy the same place as the IDW pony comics: fun and enjoyable, but not really canonical.