As noted in the comment (thank you) the update is here - http://support.microsoft.com/kb/2587147
With the recent release of MacOS 10.7 Lion customers are experiencing issues with Office for Mac 2011 including Communicator for Mac 2011. For those new to the client, be advised that this is considered to be the R2 client which is supported against Lync deployments but the Lync for Mac client is expected later this year (2011).
Monitor the Office for Mac team blog here - http://blog.officeformac.com/ which has a post from July 22 about issues known to date.
The following KB is also tracking known issues - http://support.microsoft.com/kb/2586538
If you or your customer are experiencing an issue not covered, please open a support incident such that we can investigate for possible fix.
Microsoft released version 13.1.2 on July 26. This update addresses the crashing issue on Lion.