I contemplated the same (for other reasons) but after signing up online twice for LAN's frequent flier program and stayign on hold for for what seemed like hours, and them still not issuing me a membership number, I gave up.

(For those who haven't tried, the website lets you sign up immediately, but will assign you a LANPASS number later. Much later. Over a month later I still don't have one. I imagine that if you sign up locally and not from the US it works much better, and of course, speaking Spanish is a plus.)