Most people that crunch on GPUs let their cards crunch when they are using the computer for normal usage. For more powerful cards (useful for crunching) normal usage (Internet browsing and desktop application use) does not impact the GPU crunching performance, and crunching does not impact on the GUI.

If you go back to CC1.1 cards and their buggy use a year or so ago then it was common for non-mature applications to hang and the odd temporary system freeze. Driver updates and developer tool advances have come a long way in that time as have GPUs.

Gamers can set up exceptions, so that they stop crunching when gaming, but that applies as much to the CPU use as the GPU. I would suggest that anyone playing a resource intensive game should exit Boinc altogether, as games can mess with GPU memory and even system memory.

If the WCG is still considering crunching with GPUs I would strongly suggest only supporting Fermi cards and above from the NVidia range, and would prefer the WCG choose only to support recent ATI cards, as there has never been a medical research project for ATI cards available to Boinc crunchers.

Dataman, Cunning but I would just pull that middle GPU in the summer as it still draws power, even if not in use, and it reduces system air flow for the other cards. You could disable it in device manager, but I am not sure if it would still draw power and it would still be there using up air flow space. Maybe a good time to take it out and clean it.

I guess you are using an older driver as the dummy plugs are no longer needed with the last two driver releases. The last driver also brought some performance gain over some immediately previous versions, well at least for a GTX470. That said the older (but usually buggier) drivers were faster to begin with, so the recent improvement just gained back some of the lost performance.

Ah right, get you now; I thought you were disabling it for the entire summer.

Was thinking the rendering unde Linux was not up to snuff compared to Windows, so here is another piece that will facilitate any GPU crunch implementation using OpenCL, on the agenda of WCG (approved) http://www.webupd8.org/2010/10/gimp-plugins-in-ubuntu-1010-could.html
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Let me tickmark the 8xxx series box, but also have a cheapo 220 waiting on the shelf ;-)

ATI SDK2.3 will be released in Dec 2010. By the end of the year the GTX475 should be out, and along with the GTX460, be properly supported by Linux (the NVidia 3.2 dev app has been at the RC stage for some time). So if the WCG decides to run with Open CL, around Jan/Feb would seem like a good time to begin widespread testing. The next year or two is likely to see more revisional updates and refinements rather than full generation changes for both types. So we might be entering a period of stability in the GPU arena.

Normally it's important to give yourself time to actually do some research with the existing GPU technology, before people start swapping them out of their systems; GPUs do not hang around like CPUs. A 3 to 5 year old CPU is still useful, but a 3 to 5 year old GPU is dead weight - For crunchers, 3 months running costs are about the same as a replacement card, with lower running costs. A comparable replacement could pay for itself in 6months and do the same or more work. So normally there is a window for each generation.
Open CL may however avoid this, it is well touted as being universal, but it is only universal up to the time it is bettered by code or card. There is no guarantee that the next generations of card will support Open CL, and from experience you cannot rely on what ATI or NVidia say they will do in 18months time; NVidia all but stripped the Fermis of double precision very late in the day and much to the dismay of many. Will Open CL be supported by the next generation of ATI or NVidia GPU? Probably, but not if they want to sell something else, and they very well might.
As for drivers, you can’t say 17+ supports OpenCL or anything else. You will need to test every generation of driver against every card type to be sure it actually does, and you will no doubt find that some do not, that some older drivers were faster and some new code is not supported (app mod needed...), but this is the way GPU crunching is, has been, and will continue to be.

So, is the WCG really up for this challenge?