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Well, not the best thing to do, but if you're the only user, you may never notice a thing. I doubt any app or process is going to do anything untoward that it didn't already have write or execute permissions to at the group or global level.

EDIT: Looked at my own. ~ is 755, ~/Library is 700.
 
There can be potential issues, mostly concerning security. I suggest running Disk Utility and do a Repair Permissions. That should take care of most of this, though won't undo all the changes.
 
There can be potential issues, mostly concerning security. I suggest running Disk Utility and do a Repair Permissions. That should take care of most of this, though won't undo all the changes.

This post should be remembered for all time as the only time ever, someone suggesting "repair permissions" as a fix is actually relevant!
 
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