Note: This is the shade-tree mechanic (aka lazy man) technique for temporarily fixing a drooping door from dragging against the strike loop when closing. The proper way is to adjust at the hinge, or replace the hinge completely. See first comment below from handyvorb for more info. This technique will stop the dragging, but will cause the door to be misaligned. This misalignment will be visible from the exterior with the door closed if you look closely at the belt line trim or any other trim you can compare from door to door.
On with the lazy/temp fix ...
This is a really simple DIY but I figured I'd post it since a few people were having this problem (including me) and it's a quick fix.
Symptom: When you close a door (typically the driver door sags before any other door) the latch mechanism will not meet the strike plate perfectly and you will hear a thumping sound. This is bad because it can wear the latch mechanism prematurely and in extreme cases, make it difficult to fully close the door.
Tools needed: M8 triple square socket. Depending on which one you have, you may need a 14mm deep socket and socket wrench. I purchased my triple square sockets at autozone, tools pictured below
This is the strike plate, the triple square bolts fix the strike plate to the door jamb/lower b-pillar
Here is a closeup of the strike plate, note the vertical and horizontal notches on the plate as well as the notches on the door jamb to help you remember the position if you ever remove the strike plate. Note that your strike plate is probably not going to be aligned like mine, but just remember which notches your plate lines up with.
To fix the sagging door problem:
1) Loosen the 2 triple square bolts almost entirely, allowing the plate to be moved around. Do not completely remove the bolts.
2) Since your door is sagging, that means you will need to move the strike plate down. Depending on how much your door is sagging, you may have to move it all the way down like I did. You should retain the vertical position of the plate and only change the horizontal position. Changing the vertical position may affect the ability to fully latch your door shut.
3) Once moved down, hand tighten the strike plate bolts and carefully close the door. Do not shut it completely, do not let the latch close on the strike loop as it will move the plate. Just test to see if there is still any binding. If there is, loosen the bolts and move it down some more. Once adjusted properly, tighten the bolts fully. I cranked them pretty good but did not check the torque spec. I would guess somewhere around 20-30 foot pounds.
Get in the car and open/close the door a few times to make sure everything is working properly. Listen closely to make sure the latch mechanism isn't still binding on something. It should cleanly close and open without any extra effort.
Hope this helps some folks.