My first job in publishing was with the Sandra Dijkstra Literary Agency. That was almost 10 years ago now, but I can say that she is a strong agent, will only take on work she is passionate about, and then will really fight for it.
Oh, and for those concerned about sending a package to someone who isn't there anymore, staff cycle through rather quickly there, and at least when I was there, they would just go to the new person handling submissions or that genre. The books and websites with contact info can't keep up with the staff changes, though I suppose that is the case with many agencies and publishing houses...