I don't cache things between runs of the application but once something is downloaded, I don't re-download unless the user requests it.
Huh, that UI seems very familiar.
Oh and about Voicemail support. With TOR I added to my GV API the ability to get the voicemail. I've been planning to make it so that Maemo would ask you to download the voicemail if you've gotten one. Contemplating this for DC what I would probably do is add a "Play" and "Save" button to the window that opens when you click a voicemail. I would hope I could have GStream stream directly from the GV site but unsure about permissions. I've been busy with some other audio apps and my Qt ports to work on this.