Timestamp indexes

A while back I as told (by Tom Lane I *think*) that timestamp (previously
datetime) fields couldn't be indexed as such and that I should index them
using this method :

CREATE  INDEX "applicants_resubmitted" on "applicants" using btree ( date
("resubmitted") "date_ops" );

Since almost all the queries that search that field  search it casting the
field to date, I thought that would be OK.. It was for a while (in the 6.5.X
days) but it seems that 7.0.2 is treating this different. I can't get an
index scan on that field no matter what I do.

Any suggestions?

Thanks!

-Mitch