I think it is not too early to draw any conclusions: setting the CPU to 100% and increasing the memory limit eliminated the problem, no more dead processes in my Windows task manager.

Since I changed 2 things at once, now I will reduce CPU usage to 85%, leaving the memory limit high, to see if the problem comes back. (One Rosetta process took 560 MB of RAM, uuhhh.)

Answering one thing here: now at 100% I DO feel some sluggishness in some not-so-important areas. Namely, in flash animations (eg. FarmVille) and when accessing the computer remotely.

Good news.

As I'm told, setting CPU usage to anything less than 100% can bring back the old symptoms, so look for clues that the problem is recurring (or not recurring).

On memory, I'm set for max 60% when the computer is in use and 90% when it's not in use (4Gb RAM on a W7 laptop). I have no idea if this is optimum but I haven't detected any issues with it. The settings seems a reasonable compromise to me, if that helps.

I was reminded by mod.sense some time ago that leaving little memory for ordinary programs to run may starve them of RAM and force them to use disk pagefile, which may be a reason for slow running. I'm not sure if I've remembered that correctly, but the point is that all programs should be given a chance, allowing for what they may need.

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Good news.

As I'm told, setting CPU usage to anything less than 100% can bring back the old symptoms, so look for clues that the problem is recurring (or not recurring).

On memory, I'm set for max 60% when the computer is in use and 90% when it's not in use (4Gb RAM on a W7 laptop). I have no idea if this is optimum but I haven't detected any issues with it. The settings seems a reasonable compromise to me, if that helps.

I was reminded by mod.sense some time ago that leaving little memory for ordinary programs to run may starve them of RAM and force them to use disk pagefile, which may be a reason for slow running. I'm not sure if I've remembered that correctly, but the point is that all programs should be given a chance, allowing for what they may need.

I always set my RAM usage to 95% to avoid these problems. I got 4GB which are rarely used except for when I work on heavy photoshop files, or play really long games.

And regarding OP, new CPUs are really hard to overheat, I've had my ASUS Laptop running 24/7 Rosetta and Collatz (GPU + CPU, both under same heatsink), it has never overheated. PLUS, both my GPU and CPU are overclocked (Check the fastest PC in my PC list, my little jewel :') ) And desktops have better cooling than laptops.... so you do the math.

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While awaiting the OP's return, I see there's some success among the failures now, with the failures showing our dear friend "Can't acquire lockfile - exiting". As I recall, these are remnants of when the problems were happening, but I can't remember how to fix it. Something to do with locked files in C:UsersAll UsersBOINCslots requiring Boinc to be shut down in task manager and all services stopped, boinc_lockfile deleted in each of the rogue folders (numbered, 0, 1, 2, 3 etc) then re-booting.

Can someone confirm the correct procedure or point to a link?

With some of the more recent versions of BOINC, such as 6.10.56, simply shutting down BOINC and restarting it automatically clears all the unneeded boinc_lockfiles.

On running BOINC as a service: The best I remember, this was found to be incompatible with running any workunits on a GPU instead of a CPU core. Minirosetta workunits don't try to run that way, though.

On having enough memory to run multiple minirosetta workunits at once: On two of my computers, some of the settings related to the SuperFetch feature of Windows Vista often seem to interfere with this by tieing up at least half the physical memory for something not adequately shown, and being rather slow at releasing this memory when something else needs it. However, the SuperFetch feature is so poorly documented that I haven't been able to find much on how to control it except how to turn it off entirely, which does not seem appropriate. I already have all my computers at the maximum physical memory their motherboards allow (4 GB, 8 GB, and 8 GB).