just to add a little to the first answer here... if you want consistent snapshots, then install SnapDrive onto your system, this will allowed consistency in the Windows Snapshot.
one thing to thing about iwth this is page files on boot volumes, they create a lot of data change and lots of blocks moving around, so just be aware when snapshotting about how big some of them may get.
this would be the same regardless of if you do the snap with snapdrive or just snap the volume at the storage level.
what are you trying to achieve maybe should of been the first question!