The short NEWS file extract follows, also containing Conrad's entry for 0.9.80::
0.2.7 2010-09-25 o Upgraded to Armadillo 0.9.80 "Chihuahua Muncher": * Added join_slices(), insert_slices(), shed_slices() * Added in-place operations on diagonals * Various speedups due to internal architecture improvements
More information is on the RcppArmadillo page. Questions, comments etc should go to the rcpp-devel mailing list off the R-Forge page.