I thought that I'd write up a brief guide to syncing up portals for those who are unfamiliar with how they work.
First some things to be aware of:
1] Nether portals are not permanently tied together, each time you go through it will search for the nearest available portal to connect to. If it doesn't find one it will then create one.
2] One-way portals are possible, if you and your friend's portals are too close together then both overworld portals will connect to the same nether portal. When you come back through, however, the netherside portal will only connect to the closest overworld one.
3] Portals for some strange reason can spawn above bedrock. This seems to be a new glitch.
Here are the steps to follow to get your portals to sync properly:
1] Place your overworld portal and go through. (take note of your overworld coords with F3)
2] In the nether check your coords they should be your overworld cooords/8 (some deviation is normal). If they are, good, you're done. If not keep reading.
3] Go back through the portal and see where you come out in the overworld, if its your portal congratulations you just took over someone else's portal and now they will have to come read this. If it is someone else's base then you need to keep reading.
4] Before you go back through your home portal you will need to gather the necessary resources to construct another portal. (remember you only need 10 obsidian) Once you have these go back through your portal.
5] Check F3 again, and keep it open as you make your way to your overworld coords/8.
6] When you arrive construct and activate your portal. Go through and check that you are home.
If your portal spawns in an unwanted location it is important that you destroy it before hand placing a new portal in the nether. Do this before using your overworld portal again.
Hopefully this will be helpful for some of you guys, if you have an questions or need extra help ask in a reply to this post.