Hi there,
I know you've already done it, but would like to just add my two cents into this.
I would recommend you use SECURITY GROUPS to map network drives instead of doing it on OU's. What I can see the issue can is is:
1. You'll have a lot of different OU's to manage.
2. Keeping track of and managing all your different logon scripts through GPO's and OU's just take more time
What I normally is just use ONE OU to put all my users in. Then put users in their respective SECURITY GROUP memberships. Then I do the logon script through the NETLOGON share on the DC and use that to map drives based on what groups they are part of.
Also, the other added advantage with using SECURITY GROUPS instead is that you can then use that security group to put SECURITY and PERMISSIONS on files and folders. That way, if they are in a group caled "HR" then they get the HR drive (example the H:\drive) also also they will have the permissions to access it too. This then stops users from manually mapping the shares themselves and if they did, then they can't get to it anyway because they don't have security permissions to do so.
Have a look at this example here: http://www.thisishelpful.com/kix-login-script-to-map-printers-network-drives-and-setting-changes-a3.html.