How are you going to prevent commercialization like reddit ?
How are you going to prevent a path like digg ?
I used to be on both now they are wastelands, just advertisinng portals
One of the nice things is that advertising can be in-app rather than external, for example ads for a restaurant/hotel will direct to the product in the app rather than an external link.
Only after getting a solid userbase will I start to actually implement any monetization.
Also planning to put some measures in (if the app gets big) to make it so that fake-looking users or users with just a couple of ratings don't have their ratings count towards averages and predictions.