Maintain? It's just text like comments. If somebody is spamming. You ban him, or, the IP range etc. You don't even create any content, the users are. Maintaining is not an issue in this case. The cost of this thing is minimal, it's just text, no images (you can disable avatars etc.) Here is a demo: http://www.phpback.org/demo/ it's a simple system based on CodeIgniter - so it can be tweaked pretty easy. It would be ideal for users submitting and voting of ideas for KDE and Plasma etc.
More info please.
Without it I'm going to take a stab in the dark. I assume since you want feedback this is going to be on a website. If this website runs wordpress, then I'm going to suggest a plugin: Contact Form Builder it's free for the first 10 forms or something. Works great for feedback. If this isn't the solution you are looking for please provide more info on your setup.
I haven't tried this one, but this project looks promising.
Perhaps something like UserVoice or PHPBack (or any other similar product) would be valuable to HiRez...
Wouldn't have to open it up to everybody (by invite only) but would also be able to allow those that ARE invited to suggest, and then vote on those suggestions. HiRez can respond/update/explain why highly suggested items aren't possible or their justification, etc.... could even sign an NDA if they felt it necessary.