I found this on the www.us.playstation.com forum:
We have been looking into the current issues surrounding the moderation of LittleBigPlanet levels, as it is clear that we're not currently going far enough to inform users who have had a creation moderated why the action was necessary. We are moving towards a system whereby rather than receiving a generic message any affected user will also receive an indication of what was found to be infringing on the EULA. We're additionally looking to provide clear, plain language directions on what is and is not acceptable to be published through the game.
Until these changes come in, my official recommendation is that any creations you publish do not infringe on any copyright or otherwise include language or imagery that is not suitable for an audience of all ages. We'll have more comprehensive guidelines soon, but for now the EULA states the following :
You agree that you will not create, transfer, share, send, submit or upload any User Generated Content that:
(a) is protected by copyright, patent, trademark or trade secret or otherwise subject to third-party proprietary rights, including but not limited to rights of privacy and publicity (unless you are or have permission from the rightful owner);
(b) contains fraudulent statements or misrepresentations that could damage SCE or any third party;
(c) contains any statements or materials that disparage, ridicule or scorn SCE or any third party;
(d) is obscene, defamatory, threatening, harassing, predatory, **bleep**ographic, hateful, racially or ethnically offensive, or encourages conduct that would violate any law or is otherwise inappropriate;
(e) is an advertisement or solicitation of business;
(f) is an impersonation of another person; or
(g) violates any of the rules of Online Conduct, other terms of this Agreement, terms of the PSN Terms of Service and Usage Agreement or any other terms related to this game
For the time being, if you believe your level has been moderated and you don't know why please contact me via private message including the level title and your PSN ID and I'll investigate