Hi, just thought I'd chime in on the new premium account. I'm not a very dedicated user, granted, but I use the decklists to dummy up EDH ideas all the time, as well as keep decklists of decks I am selling so I can send a link to people who are interested. After enabling my free trial of Deckbox premium, the only feature I've seen that's truly useful is the scratchpad. I always keep a list of non-sideboard cards I would like to try in the maindeck anyway, and this is quite useful. However, it's not worth $4. Moreover, the 'built' vs. 'idea' is rather redundant, as I keep all my ideas in one deck folder and all my completed decks in another anyway.
Just my two bits.