Page transitions is a free standalone utility
Page transitions are available since version 4 of Acrobat.
Beginning with version 6, they are all available in the Pages navigation panel.
In Acrobat Pro they are available as a dropdown menu : not very user-friendly since you cannot easily figure the final behaviour.
So, they must be tested one by one and this is very time consuming.
Thanks abracadabraPDF for finally providing an easy way to preview page transitions!