In my experience:
1) LUD changes, but nothing else changes (exact same messages)
2) I receive 2 emails for each approval
3) Email notification system seems to work, except my 140 approval notice changed first on the website. I received email a day or two after that
4) Once the case status message changed, but LUD did not. As it turned out, case status message change was incorrect (it was about period of time it takes for I-140 approval)
Given the randomness, I can't fully trust their online system. But it was very helpful in responding to my 140 RFE. I had a window of 20 days since I saw the RFE message online until acquisition of my company. I was anticipating an RFE and as soon as I saw the online message, I started preparing response and notified my attorney. As a result, we were able to respond before m&a mania took over!