First I want to add my vote to putting the color key under the "Stop" button. (and a higher res map if possible)
Second, I *REALLY* want a way to ignore a path, for example cache folders which aren't worth defragging.
Third, there does seem to be some slowdown when choosing to defrag many (hundreds +) files, the bottleneck goes from (soft-)IO to CPU.
Fourth, an ability to right-click on a path component in the list and select to defragment that entire sub-tree would be nice
Fifth, on the status bar it would be nice to see the number of file, fragments and size of the selection / checked files
Also a bug, the installer SHOULD NOT (As per the Windows logo guidelines) create shortcuts to its homepage (you're meant to link from inside the app) or especially its uninstaller (that's what add/remove programs is for), and when creating a single shortcut (like you should be doing) don't put it in a folder, just put in "Programs".
Other then that, *VERY* impressed.