Question about writing HDFS files

[John Lilley]

I seem to recall reading that when a MapReduce task writes a file, the blocks 
of the file are always written to local disk, and replicated to other nodes.  
If this is true, is this also true for non-MR applications writing to HDFS from 
Hadoop worker nodes?  What about clients outside of the cluster doing a file 
load?
Thanks
John