On my PC (Firefox), it has been a couple of months since I've logged in. Every once in a while something, perhaps an update wipes out all my cookies which is a bit of a pain, but relatively rare, usually occurring after a reboot or closing Firefox.

Same thing is true with Chrome on my cell phone. Rarely log in. It really doesn't like the politics forum under Chrome, and so I usually discover quickly if I find myself not logged in.

My biggest issue is some kind of a timeout, usually in Firefox. Sometimes with a post I'll start at night, fall asleep, and finish in the morning. Usually carefully hitting the back button, then copying to the clipboard and refreshing, I can recover without losing data. I don't remember if that has also occurred under Chrome, but I presume it can occur. I would still be logged in.