When going thru a nether portal while in survival mode, a perfectly timed disconnect from a server can cause an interesting effect. Disconnecting a split second before the "dirt" screen(loading screen upon going thru portal) pops up will cause your coordinates from the originating dimension to be set as your login point in the dimension you where heading to.
Example
I'm at 12631, 63, -26314 in the nether
I go thru portal, perform this glitch and disconnect
I log back in at 12631, 63, -26314 in the overword

Works both ways Nether>Overworld, Overworld>Nether

No portal is created where you load in when doing this, you just "appear"
If chunk has been previously loaded, you may load into blocks and be stuck or can fall down.
Unkown if portal is created where it is supposed to be.
Can be used easily to travel great distances very quickly.

Was not able to duplicate in Single Player Worlds, or while in different game mode(yet)