For me, it was a near real-time snapshot of the health of my mining hash rate vs. the pool hash rate.
It may take some getting used to, but can you try looking at the shifts page for this?
It shows your average hash rate in the latest shifts, and this is what the "pay per block" estimate was based on. Sure, it's 10 numbers instead of 1. But it also tells you roughly when there was a problem if you had some downtime. This is your mining health in the pool. The shifts page also shows the pool hashrate, although I think that is less useful as it doesn't affect your average earnings, only the variance.
Ok, you make a good point as to noting WHEN I may have had some downtime on a shift basis. I'll focus on that for a while... [still the one number WAS nice, but truth be told, I CAN convert my "score" to a similar snapshot!]
Just an FYI, as I live in a rural area, my "home" Internet service is actually Verizon LTE (a USB modem connected to a Cradlepoint router), so from time to time, it will "drop" -- but it is surprisingly good 95% of the time. For those of you who are wondering, my only other alternative is satellite - a non-starter due to the latency issues. I have multiple ASICs for BitCoin and LiteCoin as well as bevy of iPads, iPhones, desktops, and laptops as well as other home automation, IP cameras, and other devices all connected -- and I manage on a 40G plan (yes, I sometimes exceed that).
So, even though I'm 24x7 mining on BitMinter, 99% of the time my downtime is connectivity related.