Sorry you're having trouble! It's unlikely there would be anything of note in the normal logs. What would help us determine what's going on is taking a sample while OO is hanging (if this is still happening). This is done by using the Activity Monitor app in Applications/Utilities. Open that, and then select OmniOutliner from the list of processes and use the Sample Process option in the toolbar. This will open a new window with the report. If you get the chance to do this, please send the sample report to our Support Ninjas at
omnioutliner@omnigroup.com
If it's not happening anymore, where you doing anything else at the same time? Were you recording audio? Do you have large attachments in this file and autosave was kicking in?