I think you're talking about the official Spot site. Your tracks will disappear after a month or so unless you load them into spotwalla or some other alternative place.
Spotwalla is a separate, free service / site which allows you to maintain your tracks / trips on a site separate from the Spot site. It utilizes google maps. Once you establish a free spotwalla account you link the spot account with it, and after you complete a trip transfer the tracks to a new "trip" in spotwalla and you will be able to preserve the tracks beyond the 30 days the spot site keeps them.
I have trips on spotwalla that are several years old.