The ST_GeomFromText function takes a second argument - SRID. Therefore, if your sf_blocks level is in Lon / Lat, WGS84, then the EPSG code is 4326. In this case
SELECT *
FROM sf_blocks
WHERE ST_Contains(
the_geom,
ST_GeomFromText('POINT(-122.44107 37.750066)', 4326)
);
.
sf_blocks ( , , Lon/Lat), ST_Transform GeomFromText.