My first reaction after they revealed that it is actually the real Barney, i was like....
wait a minute....i remember Barney could barely drive....
In Season 2, Episode 17 "Arrividerci, Fiero", Ted taught Barney how to drive, and he didn't even know which is the brake and he was like going 5km per hour?
But sure, people moves on and so does Barney. This is seasion 5 now and he could have already master the art of driving, and be able to fool others to think that he is a professional cab driver.
The Robin and Don conflict is not very convincing, why can't Robin take the job and ask Don to move to Chicago together? It wasn't really a serious dilemma.
Overall this is not a bad episode, but really doesn't look like season finale.
I like the sum up from Ted that we are all Doppelganger of ourseleves.