postgis 2.0 - PostGIS2 have automatic BBOX indexing?

I need to compare millions of geometries by the && operator (BBOX).

When CREATE TABLE see geometry type on PostGIS2, it do also something like INDEX ON t USING GIST(g)? or I need to express, always, the CREATE INDEX in (or after) my CREATE TABLE?

If it is automatic, it is for any field name (or only for "geom")?

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PS: (if no index is automatically crated) when I use ST_DWithin(A,B) PostGIS generate a temporary index?