As previously stated, array support was in the works and now it is commited to cvs!
So, from now on you can start persisting array data to postgresql. Thanks very much to Jon Hanna for getting this work done.
Now, you can persist arrays and, as Jon said in previous post's comments: "Anything that implements IEnumerable<T> where T is a type already supported by npgsql will be treated the same as T, anything that implements IEnumerable<U> where U implements IEnumerable<T> will be treated the same as T[,] (but cause an error if it's a "jagged" array, as postgres doesn't support them) and so on. In order to use it, just use an array or IEnumerable<T> as parameter value."
So, let the game begin!
Also, thanks to Michael Parshin for his help fixing bugs on array type support.