Is this an infinite combo ?

A player already has Earthcraft in play http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=4756

Next turn they cast Squirrel Nest http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=31836
They enchant a land they own and immediately tap it to put a 1/1 squirrel token into play.

Question is : Can they then immediately tap the new 1/1 squirrel token to use Earthcrafts ability to untap the land enchanted with Squirrel Nest ? Then rinse and repeat until the cows come home ?

As far as I can tell this should work. Since it is teh ability of Earthcraft to tap the creature and not the creature's then it should get around summoning sickness. The think that you have to realize though is that is you do with you will have as many squirrels as you want, but they will all be tapped. This basically gives your opponents all one turn to try to kill you. In multiplayer they should fairly quickly all just gang up and slaughter you.

You could easily fix that problem with http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=45258 :-)

Or maybe just a Fog or two to delay their attacks until everything is untapped and ready to attack

Yep, its an infinite combo. Most people get it wrong because they think the creatures have summoning sickness and can't be tapped to use Earthcraft's ability.

I showed that combo to one of the DCI judges that was running the tournaments in the shop several months ago and he said the combo wouldn't work. So I had to show him the ruling I printed off of the Wizards website that said it was a legit combo.