Vista's defragmenter, unlike XP's and win98's displays no information about the disk's fragmentation state, or defragmentation progress.
However the help does say that using defrag.exe will yield more details. defrag.exe is a command line version that reminds me of linux system utilities. Remember to run it as admin. On a side note, who would have thought that Microsoft would implicitly say guis are evil?
One major improvement is that you can work while defragmentation is going on, and the process doesn't seem to affect things.