I think many people wouldn't understand why the displayed folder size is WRONG (they not necessarily understand it's outdated).
Doesn't seem something to be applied to everyone. So it should be something to be enabled on demand.
Yes, of course. It would work best where major parts of the file system are static and the frequently changing parts are either refreshed frequently or in real folders. Clearly, displayed folder sizes would be good for some but not for others' systems, so it should be an option.
Another problem is that the folder size is the total of the DISPLAYED files. Not necessarily all files are displayed, you can use filters, and other methods. Any change in this sense would invalidate the current value.
Yes, the current file-size logic could be applied to folders too. Whatever selection criteria (filters, etc.) are in use for file sizes could be used in calculating folder sizes. But if that's a problem, the total of
all files in the folders could be used. That would work quite well, as long as the labels shown to users make it clear whether it's a total of selected (filtered) files or of all files.
Consider that any geek can already do it for real folders at least www.rejetto.com/forum/?topic=6584
If you give us a symbol or macro that grabs folder sizes, we may be able to adjust our own templates to use it. However, it would seem better and faster to buid into HFS the collection of folder sizes or selected folder sizes if that option is enabled.