Engage 4wd w/o Hubs Locked

I have a Nissan Frontier with manual hubs. The other day I forgot to lock in the hubs and shifted into 4 High and drove about half a mile. The owners manual warns this will cause damage to the drivetrain. Everything seems to be working ok. What sort of damage can result?  

The only thing I can think of is that the front differential won't spin, the side gears and spiders will though.  The ring gear is what helps sling oil and keeps everything happy.  I doubt driving half a mile would have done any damage.