I'm pretty sure Joan only does occasional "specials", and Fridays nights were held down by Paul Van the Oldies Man for a while, then I think he was bumped so that Joe MacMillan could do fridays.. I think Joe also did imaging until recently too... There are enough WATD staffers and Alumni who frequent this board who will be along any second to correct me.
Ed Perry has an open door / revolving door staffing policy it seems.. people come, people go, people come back. Ed always seems to make room for someone who wants to work.
I will say that there are a few people from the WATD news department, who have gone on to bigger and better things after cutting their teeth at WATD. Laurie Kirby of WBZ radio and Alan Katursky of ABC radio news are 2 right off the top of my head I can think of.