My Recommendations for upgrades are to ensure your read carefully through the upgrade instructions, as Rob has suggested, and also the Release notes.
Consider each item in view of your own installation and decide whether they affect you or not, and take the necessary actions.
You can find both documents in knowledgebase DOC6228 here
http://www.symantec.com/business/support/index?page=answerlink&url=http%3A%2F%2Fwww.symantec.com%2Fbusiness%2Fsupport%2Findex%3Fpage%3Dcontent%26id%3DDOC6228%26actp%3Dsearch%26viewlocale%3Den_US&answerid=16777216&searchid=1366800636507
It is also a good idea to go through the Maintenance routines prior to upgrade to ensure everything is in good shape, no outstanding errors,faults or issues, databases clean etc.
Chapter 3 - Day to Day Administration in the Admin Guide covers much of this. For more detail
Search "Maintenance" on the EV Knowledge Base, and specifically :-
How to automatically back up and perform recommended maintenance for Enterprise Vault SQL databases
Article:TECH74666
and
Routine monitoring and maintenance for the Enterprise Vault environment
Article:TECH74591
I haven't done a 10.0.3 yet (coming soon!), but applying the above procedures to a number of previous upgrades has always resulted in success for me.
Good Luck comes from Good Planning
