In winter I bought Lenovo Z510 with Nvidia GT740M after checking some reviews about its temperatures. They were max. about 87C for CPU running prime95 and 72C for GPU running Furmark. I tought I can lower CPU freq and run CPU and GPU works together.
http://www.notebookcheck.net/Review-Lenovo-IdeaPad-Z510-Notebook.105627.0.html
http://www.notebookcheck.net/fileadmin/Notebooks/Lenovo/IdeaPad_Z510/Z510_Stress.png

It's an Optimus device so I can only run it with optirun command of Bumblebee, and currently it runs only with 331.38 driver. Newer ones can't detect Nvidia GPU...
I've been crunching on it since February but only GPUgrid tasks, 'cos temperatures are not the same as the ones in the link. GPU processor runs on 1058MHz and memory 1800MHz. On Furmark the GPU reaches 95 degrees before it starts to throttle down and haven't tested it for hours but never goes down 980MHz and 90C. Far from 72C on the link. While running only CPU works CPU doesn't exceed 80C. While running GPU and CPU works together, CPU hits 90 degrees and throttles down. However temperatures are about 85 for CPU and 90 for GPU on both CPU and GPU works. When running only GPUgrid, GPU is about 80 degrees. Thus mostly I run only GPUgrid tasks. Short runs complete on about 10 - 14 hours and long runs complete about 40hours.

Lifting the back of it and letting more air into the air intake decreases the temps. 5C. Notebook has a cheap cooler under it, but it helps only 2-3 degrees. Removing the keyboard gives excellent 10 degrees of temperature decrease! :D
Now I'm planning some kind of heatsink on the GPU VRM's or some holes under the case to increase the airflow around VRM's. However, there is no place to mount a heatsink inside. :(

Now, I wonder your experiences on GPU crunching on notebooks?
Also wonder Nvidia Windows or Linux drivers difference have effect on temperatures? Also can Bumblebee have effect on the temperatures? As I said I was expecting 72C, but got 95 degrees.
What can I do to decrease the temps and run CPU works too?
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Raising the back of the device has already given fresh air, as the ventilation grills under it are open. Not high quality but I keep it running on a notebook cooler.
Anyway I will go without CPU works, and sometimes switch to CPU works.
I was not planning to crunch on this device in summer but, it is doing its job enough. I'm not planning to drill extra holes under it. :)

Little update.

As the notebook got older I just opened some extra holes under it just under the GPU VRMs. Also enlarged the fan grill so that it can suck more air. Opened some are under the keyboard keys so can suck some air from there too. I bought a Cooler Master Notepal U3+ and placed the fans one for notebook fan grill, one for GPU VRM grill which I opened and one for the main grill above CPU and RAMs etc. Also I put some aluminium heatsinks on VRM MOSFET's, capasitors and some other chips. I put a copper piece on VRM chokes but that's not good enough.

Now, I'm crunching three CPU WCG CPU units on 2 cores 4 threaded CPU and 1 on Nvidia GPU. Max. temps are about 80 depending on the work units and environmental temperature.

Currently I couldn't get GPUgrid work, so GPU is crunching POEM@home OpenCL works and CPU is crunchinh WCG Outsmart Ebole Together units. Nvidia GT740 GPU is 68 and i5 4200M CPU is 74 celsius degrees at the moment. This way it's fine but I'll probably disable CPU works in the summer when the heat exceeds 30 degrees; because without CPU units GPU exceeded 85 degrees last summer. :)

The first failed component related to Boinc crunching is notebook fan. At high speeds no issue, at lower speeds it makes different noises. I wanted to use some oil but I couldn't open inside it, Sunon Maglev fans seem hard to open inside without breaking or I don't know its way. Also I broke one of the fan propellers, this lost its balance but it's running fine now.