The single biggest problem I have is finding an article again at a later time. Even if one remembers the item or list number at the time of viewing (which I don't unless I take special note) that number will change almost immediately, a day or two later the article can be buried many pages down or have disappeared altogether.
Then there's the problem of remembering the story's title so one can search for it. Say, several days later I want to revisit a story that I remember the substance of but I have forgotten its title then sometimes it's almost impossible for me to find it again (stories often have short or cryptic titles that have little bearing with their content).
There's also a similar problem with comments, if I want to revisit a comment I read several days earlier, it's often almost impossible to find—unless I've noted the handle of the poster.
Another annoyance are stories behind firewalls, the poster will have access but many of us will not. It would make sense for these stories to be flagged with a big red dot or such so we can bypass them.