PostGIS: Assign ID of point in layer A to closest point in Layer B

It seems like if you have a lot more customers than you do stores, then it might be more efficient to create a layer of voronoi polygons for the stores, then do a spatial join of customers against the store polygons.

likewise:

select A.ID as CUST_ID, (select B.ID from B order by st_distance(A.geom,B.geom) limit 1) as STORE_ID from A

Discussions about some basic nearest neighbor solutions can be found here: http://www.bostongis.com/?content_name=postgis_nearest_neighbor#120

/Nicklas