I agree completely. This is a valuable feature for server and desktop backups. For existing servers, there is often a large amount of "convenience" files on the C: drive such as a copy of i386, installation files, backups, cd images, etc. If we could simply exclude those folders, it would dramaticaly reduce our backup sizes. This has the biggest effect when you are copying the images to another device or transferring them across a WAN to keep an offsite copy. In those instances, you want to minimize the amount of space used as much as possible.
I would also see great value in this for folders containing rapidly changing data or backup files. For instance, our SQL admin always wants to use a SQL maintenance plan to create a SQL database backup, no matter what other backup method is in place. These are often written to a local data volume that we are also taking an image of. If we could exclude that entire folder of SQL backups, it would keep our incremental image files to a much mroe managable size. For existing servers, we currently have to repartition the disk to give him a space to store this kind of stuff and we don't take an image of it.
For IT consultants with a lot of customers that do a lot of different things, this could be a HUGE timesaver! It is the one feature that prevents us from recommending the product to all of our clients.
Another useful feature (lower priority than exclusions) would be a way to resize existing partitions on the fly in the OS or from the CD. A great model for this is Paragon Partition Manager. It can convert a dynamic disk back to basic and expand a partition without rebooting. It can also shrink a partition, which can be very handy. It also does disk imaging.
Josh