ACAD 2007: Is it safe to copy a DWG file to another folder or should Save As be used?

Yes you can do either save as or copy and move to a different folder. Since AutoCAD 2006 drawings are not project based where you had to reference back to a project folder.  Now if you have a lot of x-refs or Images in the drawing which is referenced in another folder then if you save as to another folder it will not affect those. If you just copy and move to a different folder when you open the drawing you will just have to re-reference to the folders they are saved in.  hope this helps.