I wish you could add pictures to a set and delete some in a set here at posterous. Sometimes i collect screenshots for example and want to add some later. Sometimes I prefer keeping them here, not at flickr etc. because i like that it’s just one entry and not many for all the pictures.
PicPosterous on the iPhone lets you add pics to an album later, but only if you created it on the iPhone. I hope they consider adding this feature to the web also.