I have a Lenovo Thinkpad W520, with nVidia Optimus. What they didn't tell me was that the external VGA port is hard-wired to the nVidia GPU, so I can't use it at all when on the Intel GPU. Choice: battery life or external VGA? To make matters worse, it's a reboot to switch between them, and since I use Ubuntu which isn't supported (although props to the Bumblebee people for the progress they've made) it's hit-and-miss if even that will work.
If the rest of the W520 wasn't such an awesome laptop, I'd be really quite upset. As it is, I just live with it and boot into Windows if I want to use a projector.
Any idea why it needs a reboot? Some MacBook Pro models have that kind of switching (integrated Intel + discrete nVidia) but don't need a reboot to switch between them. Is it some architectural thing, an issue with the nVidia drivers, an issue with Windows, ...?
Modern Mac OS X is a bit smarter about things, but I believe the original versions of Mac OS X that supported Optimus required you to restart the windowing system when switching GPUs. That required quitting all your apps, logging out, and logging back in, which is effectively a reboot for people who stick to GUI interaction.
Doing a little searching, it seems it might be tied to the hardware as well, not just the OSX version (not sure if that's a real hardware limitation or a driver issue though). The dual-GPU MacBook Pros from mid-2010 onwards have "automatic graphics switching" that does it on the fly: http://support.apple.com/kb/HT4110
You're right that the 2008/09 models required logging out/in to switch manually; I hadn't realized that: http://support.apple.com/kb/HT3207
There is a OSX tool called gfxCardStatus that can switch GPUs without logging out on the 08 and 09 models, works great on my 09 MBP, so it only seems to be a driver issue not a hardware limitation.
> I have a Lenovo Thinkpad W520, with nVidia Optimus. What they didn't tell me was that the external VGA port is hard-wired to the nVidia GPU
FWIW, mixed-GPU Apple laptops have the exact same issue (although there's no reboot necessary), external displays can only be driven from the discrete GPU not the integrated one.
I don't know about other PC laptops but I do know this is the case with macbooks, as soon as you plug in an external display you are kicked off the internal GPU and placed on the discrete one.
If the rest of the W520 wasn't such an awesome laptop, I'd be really quite upset. As it is, I just live with it and boot into Windows if I want to use a projector.