Some recent (this is July 26, 2010) update to Lucid has caused NetworkManager to wake up, on a system that has no need for it (static, permanent, wired, unmanaged network link only) and begin broadcasting via ipc-of-the-week (DBUS?) that the machine had no network connection, causing Firefox, claws-mail, etc., to start in Offline mode. Firefox and claws-mail both have obscure ways to tell them not to listen to what NetworkMangler says. I've applied those and also removed as many networkmanager packages as I could using Synaptic. I just hope the Damned thing is dead now.
I also have a laptop, also running Lucid, that kind of needs something like NetworkManager. It works so far. When it is good, it is very, very good, and when it is bad, it is horrid.