Look closely on the right side as it is closing. You should be able to see where it is encountering resistance. It might be easier to do this manually, with the GDO disengaged.

It is normal for a door to walk to one side or another as it goes up and down. As randy said operate the door manually. See if you can pin point what it is hanging up on. It may be as simple as the left track is too tight and needs adjusted out. Check to make sure all the track bracket bolts are tight etc. Make sure all the hinges are in good shape and make sure the rollers are in good shape.

If it can't be identified fairly easily, I would recommend calling someone out to take a look.

I also have this problem, but I don't think the door is rocking back and forth, at least it's not noticable. Mine gets hung up either halfway down or right at the bottom. And it creaks so loud it wakes the neighbors up two houses down when I leave in the morning (so they say). It's always been like this, since the house was new, but now it seems to be struggling more than ever to go up and down.
What do you think would cause the creaking? Is that probably related to the hanging up? I can't grease the hinges or I'll have grease dripping all over my vehicles. Any ideas?

Marineguy, oooorrrrrrraaaaahhhhhhh.

Without seeing it I would recommend that you oil the door. Use a penetrating oil. Don't use grease. Grease is only going to collect dirt, grass, and whatever else is floating around in the air. Spray all the hinges and rollers and tracks. Move the cars first and leave the door in the up position for about 20 min. to let all the excess drip off. Run the door a couple times to get the lubricant worked in and see if that does the trick. Doors have moving mechanical parts just like a car engine and they require lubrication as well.

Doorguy