[r9etb]

On a more practical note, I'm wondering what the net effect is on gravity models.

Some space missions won't care much, but others such as GPS, and various black- and white-world earth observation missions, will probably care whole a lot.

[RightWhale]

As far as GPS is concerned, they have picked a limited selection of spheroids and insist you use them. Some spheroids, they claim, are closer to the actual shape of the earth than the one you were using, which means you have to adjust their data to match your maps. Earth is very lumpy and the gravity field also, but if it is changing all the time in new ways, we have a lot of remodelling work ahead.