Well that was fun...
Up until Pinkie's rap, I was thinking that my final rating of the episode would be rather low... The first half of the episode just didn't do it for me. I feel like they should have taken more equal amounts of time for each pony trying to teach Rainbow instead of giving Twi half the episode, then stuffing the rest of them in there. It made it feel like a Twilight and Rainbow Dash episode, when it was really just a Rainbow Dash episode with the other mane 6 supporting.
This episode was saved by its gags, I think. There were some really funny spots in there, like Pinkies rap, which was cool, even if I didn't understand all the words. xD
I thought the way they finally end up teaching Rainbow is cool, and I wasn't expecting it. Pinkies roflcopter kinda came outta nowhere, though, and Rainbow didn't mention it in her little recap of what was happening during that flight for some reason... So that was a little odd.
So, overall, I think this episode had some good ideas, but took too long to get to them. If the pacing had been a bit better (the beginng was unnecessarily rushed, I feel) and there had been a few more funny stuffs, it would been great.
I guess I'll give it... 7/10. Not a great episode, but I enjoyed it.
EDIT: I see a lot of people here only acknowledging the good parts of episodes and ignoring the bad, overrating the episodes by at least a bit (in my opinion). There were some really good points to this episode, but the whole beginning just dragged me down, and sullied an other wise great second half of the episode. I wish I could just pay attention to the good parts, but I just can't help but notice the bad parts. Just wanted to make sure nobody thought I was hating on the episode...