Thinks, IMO FIS's posts have been thoughtful, insightful and not at all insensitive. I actually agree with her about MN in many ways not being equipped to deal with these situations. I do agree with you too, Janni, that MN is utterly fabulous at creating a network of support. For me the sort of immediate life-or-death situation engendered by a posting stating intention to suicide does cross a line, though - particularly as the people reading that post will in most cases, at least initially, be in a position of horrible powerlessness.
Marina makes an excellent point about closed online chat. I did think one solution might be to refer suicidal posters to a group of MNers who had previously agreed/volunteered to be available if possible in situations like this - on a closed area of the site and with a disclaimer. When I thought it through, however, I saw all sorts of reasons why this would actually be a pretty bad idea.