Sometimes mIRC will fail to tell me when I have been disconnected. I always get that "ping? pong!" thing every now and then in the status window, but when they stop coming, mIRC just sits there like everything's fine. I either need to send text or ping someone before it realizes it's been disconnected. If I do not send text, it can go as long as two hours or more before it finally sees that I have been disconnected.

I spend most of my time connected to sorcery.net, if that helps.