Update: Latif Khalifa reports encountering the problem on Singularity, so the issue is likely to affect V1-style Viewers as well, and provides a potential workaround for those encountering the issue (see comments, below).
There have been a number of reports of mysterious Viewer crashes of late, specifically in relation to file operations (saving a texture or snapshot to disk, attempting to upload, setting your cache location, etc.).
The problem appears to be manifesting itself in V3-based Viewers, and the culprit appears to be Microsoft Skydrive.
A JIRA has been raised on the issue in general (VWR-28843), with reports that uninstalling Microsoft Skydrive eliminates the issue. This is obvious not the best solution for the situation, but those experiencing the issue may wish to check the JIRA and consider WATCHing it.
With thanks to Innula Zenovka.