1. Carpooling: zimride.com
2. Comments Aggregation: backtype.com (sort of, perhaps this is one not actually done)
3. Social Goals: 43things.com
4. Feedback for Startups: could be done with getsatisfaction.com and surveygizmo.com (in fact I've used surveygizmo.com's API to offer incentives in RateMyStudentRental.com for completing the survey, took about 15min to setup)
5. Food photos: there are actually many more than I came up with initially, just scan the rest of this thread (http://news.ycombinator.com/item?id=1366785)
6. Integrated Blogging Environment: Tumblr.com does most of that, then there are also apps like the ScribeFire extension for Firefox