Today I tried to understand the simplest things about shells in ellipticals; they all appear to have been identified by eye, and there don't appear to be any good quantitative, objective measures of their abundance. Doesn't bode well for inferring an interaction rate from shells without massive work in the SDSS. I did make this picture of a shell galaxy, however:
Note that, going outwards radially, the shells alternate north-south (plausibly), as predicted by Quinn (1984). Also note the ("minor axis" according to Balcells, 1997) dust lane and "arm" of star formation, strongly suggesting that the event which caused the shells also included fuel for star formation.
I also worked out a bibtex style file that does somewhat apj-like citation in text, but makes an annotated bibliography with displayed article titles, abstracts ("abstract" in the ".bib" file), and annotations ("note" in the ".bib" file). This hacked up bibtex style file is available on today's research page. Also under NYU CCPP CVS in "hoggreview/accretion".
Finally, I outlined my review. It is not ready for prime time by any means.