I have sent personal thank yous to every person I met with at each law firm (via email). I try to include at least something we discussed, and try to affirm my interest in the firm. I have gotten offers from essentially all the firms I interviewed with. I think it's rude to ignore anyone you met with, and only email the "important" people. Of course, if you really connect with someone, send them a longer email. Also, I only email recruiters if I met with them for more then 5 seconds (otherwise it just seems weird). I go to a good school (CCN), but my grades suck, and I have five V5-V20 offers. So interviews and the impression you make can definitely make a difference, at least in my experience.