I was wondering if there are any examples that consist on basic geolocation input and database retrieval of given inputs within a certain area, preferably the user's current location.
Here's a quick overview of geospatial queries in MongoDB:
You have to insert location information in your collection via 2D array
db.example.insert( {"location": [x,y], "category": "restaurant"})
Set up a geospatial indexes on the collection by indicating the location field with "2d" option.
db.example.ensureIndex( { "location" : "2d" } )
Now the collection will have an index which all geospatial queries will be done against.
To query for locations nearby a point (i.e. the user's current location), use the find() command with $near operand on the location field giving the point coordinates (i.e. 100, 100.)
db.example.find( { "location": { $near : [100, 100] } } )
To find users current location, you would need higher level application support to get the user's current information.
For more information:
MongoDB documentation: http://www.mongodb.org/display/DOCS/Geospatial+Indexing
The $near operator: http://docs.mongodb.org/manual/reference/operators/#_S_near