It would be useful if Subscriber supported Growl as a notification method.
Supporting standard keystrokes like Cmd-Left in the text entry field would be nice, too :)
More worryingly, what is amber.x-dns.com? Subscriber tries to connect to this at startup - probably just a version check (but there's no option to disable this, and there should be). If you deny connections to this address, email notifications don't work. In fact, Subscriber doesn't even try to connect to my mail server. Is it trying to send email via x-dns.com, and if so: why, and what guarantee do we have that our email addresses aren't being harvested? It doesn't inspire confidence :(