Kyteflyer, I currently store my calibre library in Dropbox so I can access it anywhere.
I've had a look at SugarSync's API and it requires more work than I anticipated. I'll continue looking into SugarSync but I don't think I'll have it done for the January update.
I had asked whether anyone was interested in Google Drive as a second "cloud option" for Marvin because it has a more straightforward API (as far as I'm concerned). GD doesn't seem to interest many so I'll probably put it in the "nice to have" feature bin for now.