How is mRNA directed out of the nucleus to its ultimate cytoplasmic location?
There is a complex progress involving many proteins that directs RNAs to the nuclear pore complex and ensures that they are moved into the cytoplasm. Below is part of a diagram (edited) from a Nature review article on this topic, showing the transport of mRNA. It is available from the authors online. 



Another general review with an illustrative poster is by SR Carmody and SR Wente, and can be found in the Journal of Cell Science.

As far as I am aware, interaction of mRNA with cytoplasmic ribosomes occurs by diffusion. Direction of the ribosomes to specific locations, such as the endoplasmic reticulum, can occur, but is generally through recognition of features of the nascent peptide after tranlation has started. The Wikipedia article on protein targeting provides an introduction to this area.