Well... One thing job sites are very hesitant to do is qa. Jobs that aren't jobs. Listings without salary brackets. Where I live (Dublin) most jobs on job boards don't even mention the company name. This is because they're posted by recruiters that way, to avoid being routed around or tipping off the competition. Often the job doesn't exist, they're just resume fishing.
LinkedIn has similar issues.
I think there's hay to be made just on requiring a minimum amount of (ideally structured) information.