I also spend time looking for this type of site, especially on weekends when I want to know what's on around me.
This type of space can be split into a few areas:
- Advertising (business or service)
- Calendar of events (what is on in your local area in a certain date range)
- Reviews (what you thought of a local business, event or place of interest)
- Recommendations (where to go for fun, food, entertainment etc.)
There is a site in Australia http://www.truelocal.com.au/ which covers the review/advertisement space, which would worth wile for you to look at.
My own opinion as to why this space doesn't already exist is due to lack of technical skills. If you look at many local web sites (including for many small local business), they are rarely updated and quite low quality.
I would suggest to improve on this situation you provide a set of tools that are easy to use and look great. Make your site about building a community rather than building a place for business and groups to advertise and the community will look after keeping the information fresh.
The Stack Exchange network (see links in footer) that this site is built on is the perfect example of what you are trying to achieve: good quality tools, good quality community. If you can adapt that to the local space then you are on the right track.