I wonder how difficult it would be to obtain this statistic for real-time display?
IMHO it is the only statistic which shows the degree of fragmentation,
in particular the vulnerability to future fragmentation.
If 1% of files (when there are, say, one million on the volume) is fragmented,
the system will be very seriously slowed by 10,000 files in, say, 100 average fragments,
so "1% fragmentation" is highly misleading.
Under 100 free space fragments would be a fairly good result.
Sorry if this has been said here before - I haven't had time to search.

Is this being seen at all by the developers?

Is what I ask an impossibility?

I would have thought that the information could be drawn from the analysis data, since that is used to draw the visual map.

I would think it takes into account the total amount of fragmented files. I ran a defragmenter a few years ago when I have thousands of pictures on a drive. It said the drive was 1% fragmented, but recommended defragmenting because of the amount for fragmented files. Seeing how that was back using Windows 98, I would think that kind of system would be kept running.
If I remember correctly, it was the Norton Defragmenter that said to defrag.

Yes, that was "SpeedDisk", an excellent product neglected by Symantec after they bought Norton. It was Win9x only and their attempt at NTFS was rubbish. I just trialled "Norton Utilities v11" and the defrag shows no information at all, like the provided Vista one. At least the provided Win9x one admitted it was a cut-down SpeedDisk by acknowledging Symantec copyright, while the NT/2K/XP one admits that it is a cut-down "DiskKeeper", copyright Executive Software.
None have counted free-space-fragments, AFAIR, except a few ChUI defraggers.

For your information...
This statistic is included in the command-line verbose operation of the defragmenter included with Vista.
It has more options than the one with XP, e.g. -c to defrag (not analyse) all hard discs.
It is 226,816 bytes (XP one 25.088 bytes) because it does not need dll's so they are not locked.
Here is a typical verbose analysis after a full Defraggler run, still leaving eight fragmented files and 1,172 free space fragments.
However, running Defraggler twice more got that down to 142. Running Ms Defragmenter was not as effective.

C:\Users\mike>defrag c: -v -a
Windows Disk Defragmenter
Copyright © 2006 Microsoft Corp.

Analysis report for volume C: Vista

Volume size = 31.06 GB
Cluster size = 4 KB
Used space = 20.94 GB
Free space = 10.13 GB
Percent free space = 32 %

File fragmentation
Percent file fragmentation = 0 %
Total movable files = 113,534
Average file size = 233 KB
Total fragmented files = 8
Total excess fragments = 15
Average fragments per file = 1.00
Total unmovable files = 28

Free space fragmentation
Free space = 10.13 GB
Total free space extent = 1,172
Average free space per extent = 9 MB
Largest free space extent = 4.20 GB

Folder fragmentation
Total folders = 19,716
Fragmented folders = 10
Excess folder fragments = 42

Master File Table (MFT) fragmentation
Total MFT size = 146 MB
MFT record count = 114,181
Percent MFT in use = 76
Total MFT fragments = 2

Note: On NTFS volumes, file fragments larger than 64MB are not
included in the fragmentation statistics

You do not need to defragment this volume.

C:\Users\mike>

Just to keep this thread visible to the developers!

Just pulling this thread forward again.
Be nice to have a response.