The WMG120 has the appeal of providing a compact little home file server and wireless router that is also able to serve media content. But much like my conclusion on the state of Viewsonic's WMA100, I think that the WMG120 has potential, but needs work.
I found the user interface flakey or lacking important features and the documentation needs an overhaul. The lost signal issue would become a real annoyance in day-to-day use as would its occasional failure to provide Internet connection after being powered up. These are basics that any router must satisfy and the WMG is no exception.
If Viewsonic is serious about being a networking product vendor, they'll have to be more attentive to security. It is simply not acceptable that the WMG's admin function is exposed to the Internet by default and "protected" by a well-known and obvious password. Port 80 is one of the well-known ports in every port scanner's list and unprotected WMG's would be detected (and probably compromised) within minutes of being attached to the Internet.
Just as important an issue is that the server portion completely lacks any ability to set file or user permissions. While this may be ok for use as a media server, it severely limits the WMG's usefulness for file serving or backup.
Fortunately, these are all areas that Viewsonic can address with firmware upgrades, which I hope it will do soon. In the meantime, your WMA100 would probably be better served by the software included with it, or other UPnP servers - now that you know what subnet to use.