Okay - got to more careful about how I ask the question!
On a PC, when you open a file, you are 'logged' into the folder which contains the file. So if you do a 'save as' (to make a new copy of your file), your new file automatically goes into that folder.
On a MAC, when you do a 'save as', the operating system remembers the folder that you last 'saved as' to, and defaults to that.
In our office we have a folder for for each project, and then a system of sub-folders, sub-sub folders etc. for correspondence, cad drawings, layout files etc. These are the same for each project. So when you're in 'Finder' it would be really useful if 'Finder' displayed the path at the top of the window so you could see whether you're about to save to 'Current Project/CAD/LAYOUTS' (which you want) or 'Yesterday's Project/CAD/LAYOUTS' (which you don't want). Finder is only telling you you're in 'LAYOUTS' which is too little information. Is there a way of getting finder to display the complete path of the folder it's going to save to?
Clearly, if you take your time, and you're really careful, you can pan back along the folders window and check the root folder (i.e. the project number), before you save - but if you're in a hurry (which we mostly are), you keep saving files in the 'wrong' folder.