Ah, Andorra. On my quest to set foot in every European country, I spent a day there in 1998.
It´s an agglomeration of a few Pyrenean villages which happens to be a sovereign state. Yes, The French President and the archbishop of La Seo de Urgel are co-rulers, but:
>>>However, they don't actually control Andorra any more than the Queen controls Britain!
Substitute "Britain" with "Australia" and you get the idea
Their money stems from tourism and being a tax haven. Bus loads of tourists pour into the country to do tax free shopping.
The main access route is from Spain; the only border crossing to France is not more than a side road. There were plans to build an Andorra airport near Seo de Urgel; the land needed was to be traded from Spain in exchange for an identically sized Andorran chunk. But somehow I haven´t heard anything about that proposal for quite some time now.
Official languages are French, Spanish and Catalan. Currency used to be Franc and Peseta, now it´s the Euro. However, since Andorra never bothered to formalize this currency union with France and Spain, they are not allowed to mint Euros of their own (unlike Monaco, San Marino and the Vatican that have such bilateral agreements with France and Italy, respectively).
The Andorran government is currently in negotiations with the EU to change that, but the EU uses the minting rights as a bargaining chip: they want Andorra to stop being an off-shore tax haven which drains money from EU states with (higher) taxes. Since both sides don´t budge a milimetre, I don´t really see Andorran Euros in the foreseeable future.
So "Andorra has one foot in the EU and one foot out." is not really correct.
Postal services: both La Poste from France and the Spanish Correos have set up postal administrations in Andorra. This leads to the interesting situation that there are Andorran stamps issued by both La Poste and Correos. It was even more interesting when these stamps were in different currencies.
Oh, and finally an interesting trivium: the country with the highest limit for coming of age is Andorra: 25 years!
That´s all I can come up with from top of my head.