This attic floor of 2x6 joists on 16" centers had found insulation of a relatively pleasant form of cellulose, up to the tops of joists, R18. The cellulose is compacted to give space for kraft-faced R11 batts. Unfaced R19 batts cross joists to complete an upgrade to about R45. A vapor barrier is acceptable anywhere it will remain securely at temperature above the dew point. It is nice to not place unfaced fiberglass against the cellulose, where picked-up batts would again raise cellulose to the surface.
(Edited at 11/13/2009) The claim of R45 is high. I will call the compressed cellulose R13. Applying my Insulation Math, consider parallel paths for the thickness of 2x6 floor joists.