Actually trog, I find a lot of LR atomisers just stop stone cold dead - the "regular" atties tail off like you said.
I'll certainly back-up what the good Prof says about the LR atties. I've had three now which abruptly stopped working after giving around three to four weeks roughly of good service each - which I don't think is bad at all. In fact, I prefer it that way - you know where you stand and all I do is carry a couple of spares around with me. None of my LRs have simply faded away, they've all gone out with a bang.....
As for the standard atties, I've had ones that have begun to conk-out after a week, making them pretty much unusable. Then again, I've had some that have lasted pushing two months before really tailing off. Some have started off weak, and remained so, whilst others have gone like the proverbial freight-train from the off. It's the luck of the draw......

John