The Annocryst SUM is based on the work of Jane Hunter et al, as described in 'Collaborative Annotation of 3D Crystallographic Models' submitted to ACS Journal of Chemical Information and Modeling, May 2007

an interesting paper to follow up on for the revision of the annotate service genre is:

Agosti, M. and Ferro, N. 2007. A formal model of annotations of digital content. ACM Trans. Inf. Syst. 26, 1 (Nov. 2007), 3. DOI=  http://doi.acm.org/10.1145/1292591.1292594