There is an issue with the Lenovo switchable graphics the specifically the Nvidia display driver. When you attempt to place or receive a video call the Lync client will hang. This is due to a problem in the Nvidia display driver. A forum here discusses that issue http://forums.lenovo.com/t5/T400-T500-and-newer-T-series/T520-With-Nvidia-Optimus-enabled-Microsoft-Lync-crashes-when/td-p/415799
Lenovo has not been updating their site with the current Nvidia drivers. If you go to Nvidia directly and download the current driver the issue is fixed. http://www.nvidia.com/Download/index.aspx?lang=en-us
I have a Quadro 1000m display driver and I can confirm after installing the update directly from Nvidia the issue is resolved.
Lenovo has been doing some work on their support site and the drivers that are listed there are not current. Microsoft has placed a call in to Lenovo to find out what is going on. They were told that the website is being updated. I think this is a major issue for a company as large as Lenovo. The drivers should be kept current. The driver listed for my machine (Lenovo W520) on the Lenovo site is from June 2011. The latest driver from Nvidia is August 9, 2011.