I believe significant performance benefits are to be had on LJ by removing all the formating BML in favor of CSS - right now the server bears all the burden of applying the formating translation and this can effectively be relocated to the client (where it belongs) - at LJ's traffic volume this would be a significant performance saving.
This requires that someone pass through the htdocs/*.bml, bin/.upgrading/s1styles.dat, cgi-bin/bml/schemes/*/* et al. and create a css heirarchy for the various schemes.
I am doing this now for my own installation - if Brad agrees, then I can do this work for the general case and provide the patches - my eta. would be May given my other commitments this year.