Interesting idea...Some observations though -

1) We (currently) have no way of writing data to the disk whilst in the car. This is something that we talk about a lot (and not just for GPSapp), yet have not resolved.

2) The Traffic Camera sentry would really only be useful in the UK, and other parts of Europe where they are prominent. Getting a database would be an issue as you have pointed out. In the US, most enforcement is done from patrol cars. Yes, there is a website that attempts to list hotspots that officers prefer, but ISTR that it doesn't have long/lat information, and that some of the entries are rather vague (eg... "Southbound between exits 21 and 13 of I128 from 9-11pm" or "Between the Exxon and McDonalds on Somelittle Road in Somelittle Town"), so is pretty useless.

3) Being able to flag other "places of interest" have been mentioned before. Many of the generic ones appear in various map databases, which again is an issue that still needs to be resolved.