So, I've been having some weird issues with nether portals. In my main world, I built a nether portal, travel through, collect some glowstone, travel back. . . and wind up nowhere near my base. Like, a new portal was created, several hundred blocks away from the original one, solely so I could spawn there. I didn't have a map with me; if there wasn't a big landmark near the portal I would've been screwed.
And tonight, I was exploring a swamp in my test world when I found a naturally generated nether portal. Stuck in the leaves of a tree was a nether portal, fully operational, everything. It didn't go anywhere intersting, but. . . wow.