I would go with the multiple location documents (File...Mobile...Locations). You can select (Click once) on 'Office', or whichever location is your default, then Ctrl-c to copy and Ctrl-v to paste. Select the duplicate location document and click "Edit Location".
As already mentioned you can change the "Location name:", e.g. John Smith (Network); the "Home/mail server:" in the Servers tab; the "Mail file:" on the Mail tab; and then on the Advanced tab click the flashlight icon under "User ID to switch to:" and browse and select that users id file.
After setting up each location document, whenever the location is changed, e.g. from 'John Smith (Network)' to 'Bill Jones (Network)', the system will automatically prompt for Bill Jones' Notes password.
One last suggestion - in File...Preferences...User Preferences...Basics Tab - Startup Options - check the box "Prompt for location". That way, if the 1st shift user closes Notes, the 2nd shift user launches it; a dialog box will pop up with a list of all the locations; and when the user selects the appropriate location they will be prompted for their own password. The dialog box will appear each time Notes is launched. Otherwise, if the 1st shift user does not close Notes, when the 2nd shift user comes in all he/she has to do is switch locations and they will be prompted for their own password.