Ghosth, you know what I meant, sir.
I change sides, but I don't bring the info about CV locations, etc with me, or use it. Usually I just look for the largest enemy dar bar with the smallest friendly dar bar and head to that area to get into the fight.
I don't log in with a war winning strategy, log locations of fleets and such and then switch sides to exploit it. Most times, when I change, the first clue anyone has is when I run into a former countrymate who I was fighting alongside an hour before, but I run into them in a totally different area of the map. If they ask why I changed sides, I will tell them I did it to help even the sides, which is true.
The majority of the time, I make it a point to not fight against the country I was just flying with. If I go from rook to nit, I fight the bish, nit to rook, I fight the bish, etc. Fewer hard feelings and accusations of spying and such if I do it that way.