I've noticed that when using a nether portal, it will take you to the nether as usual, but when you try to get back to the normal world, you will appear in a random cave with a random nether portal. I'm wondering if anyone else has had this problem or if its just me.
http://www.minecraftforum.net/viewtopic.php?f=35&t=100322
http://www.minecraftforum.net/viewtopic.php?f=35&t=93046