I don't know what you mean by centralized - there are over 390 IRC networks running on over 3687 servers. Some IRC networks have over 50 servers, many in different countries. Gnucleus cycles through networks and servers - it tries connecting, if it can't, it tries another one. This works automatically for host finding, and it would probably work OK for chat as well if it was done in a linear, logical fashion. Edonkey2000 uses IRC as well.