If you'd like my crackpot opinion I go into it in detail on the pinned topic but basically I believe your consciousness moves on to wherever it goes to after death, while the energy that animates you is absorbed back into some sort of collective energy pool,call it "God" if you will..
This collected energy generates new souls. Since that energy lives with people their whole life it can't help but absorb some of their intelligence and memories. Sometimes people will recall some of a "Past Life," but it's not really their past life and it's not the same soul. It's merely a fragment of memory left over in what ever piece of the collective energy that person was born with. This explains why some people have past life memories and others do not..
It also solves one problem standard Reincarnation theories can't. With the population increasing where would new souls come from if we're all being recycled?
The answer to me is that we aren't of course, we're merely using bits and pieces of energy that others have already posessed. The soul you posess now is uniquely yours and will never be owned by another. But a thousand years from now maybe someone will use your cast off energy and gain a small fragment of your memory, and maybe they'll think they were you in a past life just like some believe now..
Oh well, that's just my point of view..