The subscriber plum that I've used the most has been the ability to see stories up to twenty minutes before they are seen by everybody else. When this happens, the story header's backgound is red rather than the normal slashdot green and the story says that it will be posted in the Mysterious Future.
As CmdrTaco Expains in his journal, when a story is visible only to subscribers, no comments can be posted to it yet. This would allow the editors to still yank the story. This is interesting to me because subscribers could theoretically report problems with stories such as dups, broken links, and typos and they could be corrected or the story could be pulled. CmdrTaco has taken quite a bit of heat in discussions for making people pay to be proofreaders, but I don't see it this way. I'm happy to help out as a subscriber.
Although it seems that I refresh slashdot constantly, I don't actually see most of the stories before they get posted. I have not yet caught a single duplicate story (although at least a couple have been posted). I have tried to report problems with stories on three occasions. This has met with mixed success. On two occasions the the story was actually posted before editors could get around to correcting it.
For reporting errors, CmdrTaco announced a new email address: daddypants . The address goes to somebody on duty who can correct stories. I've used this address on two of the three occasions. It seems to work fairly well, and I have gotten personal responses from the admins about the problems I have found.
The first problem I found was that a link went to a story that had moved to the archives. I found the new link and emailed it off. The story was posted before the link was corrected, but it was simply corrected without an update.
The second problem I found was an unclosed link. The problem was corrected before the story was posted.
The third problem I found was an article linking to bugzilla.mozilla.org. Bugzilla can't handle a slashdotting and they check the referrer for slashdot.org and deny links. Timothy went ahead and posted the story anyway. It turns out that he had been using https://slashdot.org/ which wasn't blocked. Of course once the story was posted, nobody could get to the article and bugzilla soon went down under the load anyway. I found a mirror for the article and sent it to daddypants. It didn't get there in time, but Timothy put an update on the story. As a result I also filed a bug in bugzilla to block slashdot better. I can't link to it from here for obvious reasons but the bug number is 198305. From now on slashdot editors should see the failure when they link to bugzilla.