The first time I used BOINC, I had a hard time getting it running. Oh installed all right, and ran the tasks, but overnight it did nothing. New machines and I tried again with you. All ok until I installed Mountain Lion on my iMAC. Average host credits fell from 4700 to 3200, but are now creeping back.

I just don't want to keep the machine on if it is doing no work. The activity log shows tasks starting, stopping and uploading, just no credits being accumulated. Could this be just some statistical anomaly?

Black aka 20026 is dead and will never come back. I you have any work assigned to it, it is best that it is relocated. Black aka 25989 is also losing average host credits. It turns out that it was turning itself off because it was too hot, over 95F, in the computer room. But it has been running for three straight days and the average credits is still dropping.

I tried to merge the two Blacks, after all they are the same computer, but BOINC said no.

Your two computers are running well and successfully returning results. One possible reason for part of the drop in credits is the lasieve14e app. I started using this app about a week or so ago. These workunits use less memory and are thus awarded a bit less credit. For maximum credit on your computers, I would recommend disabling the lasieve14e app.

It's just that when I used to get 30 mpg and now get only 20 mpg, I am concerned that something is wrong. I was just using credits as a CPU utilization metric. Ah well.

May I suggest that if they are participating merely to
accumulate "credits", then there are better things they could
do with their CPU time.

One should participate because it (hopefully) helps advance
the art and because one is interested in the subject.

Mere accumulation of "credits" serves no useful purpose.

I strongly disagree. One should participate because they enjoy it. That could be because they enjoy advancing the state of the art, because they are interested in the subject, or because they simply want to cream their friends in a race to 5 million credits. All are equally valid reasons to participate, and all are welcome.