A little script for converting tweets with geocoords to geojson format. (The script assumes that you've flattened the tweets down to a CSV format with the field format described in the tuple of the "for" loop, which is easy enough to do.)

gistfile1.txt

import geojson
import sys

lines = [line.strip().split("\t") for line in open(sys.argv[1]).readlines()]

features = []
for (x, y, _id, text, screen_name, utc) in lines: 
    props = dict(text=text, screen_name=screen_name, utc=utc)

    features.append( geojson.Feature(id=_id, geometry=geojson.Point(coordinates=(x,y)), properties=props) )

feature_collection = geojson.FeatureCollection(features)

print geojson.dumps(feature_collection, indent=1)