I'm (quite happily) tied to Postgres because I'm using PostGIS, but the ability to add freeform data to a location would be ideal. Looks like I may already have a solution here.
I'm building a 'taxi tracker' app, for want of a better term- gives you estimated trip times, allows you to share the journey with other people so they know where you are.
That part doesn't require PostGIS as such, but it's for an NYC city government app competition, so we have all sort of city datasets to use. I've used PostGIS to help make custom map tiles (preview at https://twitter.com/#!/taxonomyapp/status/149565007384940545), highlight the outline of the building you're heading to... all sorts. It's been a fantastic learning exercise.
I don't know exactly what your GIS needs are, but it might be worth seeing if MongoDB's geospatial indexing meets them if you are interested in querying free-form data.
@scorpioxy -- I can't reply to you directly, but you've been [dead] for a few months now. I see you've posted quality comments, but you posted what could be perceived as a spam post 138 days ago and so you got marked as a spambot. But you're clearly not. Might want to clear that up, but for now, you're dead when you probably ought to not be.
