Sukrim gave a good summary.  Generally Eligius should have a a utility of 1.0 (unless they have had a series of long rounds and run out of credits, then they switch to proportional like most other pools.)  Oddly my Multipool stats pages gives them an efficiency of 0.826 based on four non-pending blocks.  It might be because of their server problems and upgrades.  

Eventually readily available pool hopping software like MultiPool should drive all pools to adopt similar scoring strategies to Eligius.  Before this, there was only a limited group of people doing pool hopping at the expense of everyone else.  This kind of software levels the playing field, and pushes the pools to improve their scoring systems.