I scratched my head over this advice from John Jantsch over at Duct Tape Marketing -- until I realized John's audience is small physical businesses, not direct marketers. He wrote:
Tripling or quadrupling your lead conversion number is usually the easiest thing to do once you start paying attention to it. It's much harder to triple the number of leads so focus on what you say and do on the phone and across the desk, prepare marketing materials that over educate and get everyone in your firm on the same page when it comes to telling the value proposition you have.
It is the opposite situation in direct marketing.
It is usually far far easier to double leads (increase circ, rollout more keywords, rent more lists, join a new coop, test alternative media, etc.) than it is to double conversion (response rate, site conversion rate, etc).
Raising conversion rate is hard. That doesn't mean marketers shouldn't obsess on improving site conversion or catalog response rate; we all should. But the quickest,easiest, more direct (pun intended) way to grow top line is by getting more qualified leads.