Opening up of anything on to the internet leaves a risk be it UPNP (as you've helpfully clarified for me

) or from just basic web servers (as ajaxamp, hrequest, etc operate as). Maybe I could just go evil and create an FTP server from within Winamp and leave it as that

But being serious about things, whatever is done, the security of the setup needs to be thought about from the get go instead of trying to patch it in afterwards (i.e. trying to make use of HTTPS connections instead of HTTP).
And going back to original request, something like airdroid (which has been in the news recently for it's security related issues) might be an option to what I've already mentioned from the dropbox, etc options..
-dro