How to fix lsregister failing associations after reboot?
The LaunchServices database is built with data from as many as four domains. (See 'lsregister --help' for more info on these domains.) You might not be rebuilding the LaunchServices database correctly.  This is the command I use to rebuild the database on my Mac:

sudo /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user


If you really want to get into the nitty gritty of file associations (plus a whole lot more) and want a nice GUI to boot try installing RCDefaultApp.

http://www.macupdate.com/app/mac/14618/rcdefaultapp