Although neither the tutorial nor the kml 2.1 taglist is really clear about this, statements in this thread point out that the targetHref in an Update tag must be given as a full absolute path.

The use of relative paths could really improve animations, even better than the Timed animations.
Have a look at the beautifull Soyuz Launch of JPW . It is really well done, but mind you:

• the soyuz model is loaded about six times
  
• other parts of the animation are als loaded multiple times
  
• therefor the file size is very large
  
• there is no movement in the point of view
  

A relative targetHref would enable you to put the whole lot in a .kmz and refer back and forward to the files contained in the kmz.

Imagine:

• the doc.kml contains two networklinks
  
• one loading the soyuz -model
  
• one updating the soyuz-model to its first position;
  
• This update-file (update1.kml) would not only
• update the position of the soyuz-model,
• but also change its own href to the next file (update2.kml) also present within the kmz.
• Besides it could add a new lookat to fly to.

So with each model only loaded once, a sequence of update-files (update0.kml - update999.kml) all within the same kmz could make a great show.
All this is only possible when the targetHref is made relative.

Please GoogleEarthTeam, lets move!