Open Live Writer uses several registry keys. For a complete uninstall, you should delete them. They are located at HKEY_CURRENT_USER\SOFTWARE\OpenLiveWriter\

There are several keys of special interest:

HKEY_CURRENT_USER\SOFTWARE\OpenLiveWriter\Updates
For automatically loading the nightly builds - use this carefully as we may be unsuccessfully testing a new feature, create a dword key for CheckForBetaUpdates 1 = beta, 0 = regular

You can turn off automatic updates by turning off AutoUpdate, change the DWord key to 0

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows Live\Writer\Weblogs
Stores the location and information for your weblogs. Many users have copied the entries from LiveWriter rather then reenter them.