I created an image of the C: drive, Windows Vista. The image is 7 GB in size. Then I immediately installed a printer driver that was 10 MB in size and immediately created an incremental image. The incremental image file is 668 MB in size. Why so large for such a small change on the C: drive. I don't think it was the bug that has been documented on another thread here, (which I have experienced on a different machine) since it did not do the long reconciliation that is characteristic of that problem.
Thanks