I haven't used PostCard, but for the people wanting to use this application solely as an iCards alternative, there is PopCard.me. It does almost everything iCards used to do and be. It offers a simple web interface where you can select standard pictures to make your own greeting card, the text on which will be nicely anti-aliased. When sent, the receiver only gets a JPEG of the card you sent, just like iCards. There's one difference, however, which makes PopCard.me even better than iCards: it's connected to flickr, meaning you can make a card from any flickr photo with a Creative Commons license. Very nice.

I found the service a little while ago, while searching for good iCards alternatives. Well, not really alternatives, as iCards is long dead (may it rest in peace).