Much like over-long opening credits, long closing credits say a lot about where the filmmaker's focus has been. Usually: not on the film itself. And since nobody wants a burger that's all bun and no patty, here are some words of advice from our countless hours sitting in front of short film submissions.
1. No bloopers. Seriously, we're glad you guys had a fun time making it, but keep the outtakes for your cast and crew who are better able to appreciate them. An audience is just waiting for the next movie to start.
2. No long moody fade-outs. If you have an original score or a song you'd like to use to send the audience on it's way, that's great; keep it under 30 seconds. Using the end credits as a kind of denouement is fine for feature films, where the audience has already committed a couple hours of their time, but if your film is 5 minutes long, we don't need 2 minutes to come down from it. We're waiting for the next movie to start.
3. No interminably-held stills of cast & crew names. As with the superfluous "starring" lines in opening credits, chances are good that we don't know any of the people in your end credits (hell, we don't know most of the people in the end credits of Hollwood movies!). So get your scroll on and be done with it. There's another movie after yours.
On the positive side, screen credit is one of a very few things (along with food and copy) that struggling, cash-strapped filmmakers can offer to those working hard for little or nothing. And crediting those who have made your film possible is extremely important, both karmically and for the more earthbound practicality of getting good people to work with you again. That said, if a viewer wants to follow up on who your gaffer was, they'll search for your website.
The truth is, if we're screening a block of short films and the credits start to run a little long, we'll just cut them off. It's not personal, and if you're just doing it to look professional, it really doesn't. It looks like you don't want your movie to end. And ultimately, if you haven't made a good impression by the time the end credits start to roll, well, it ain't gonna happen.