I got my is220 about 6 weeks ago and it was running fine until 3-31/2 weeks ago when is started losing coolant, I thought it was a leaky pipe connection so I changed the clip, it didn't solve the problem and I was then hoping it was something simple to fix. I booked it in for a service and had that today (7/4/15) and found out it was the dreaded head gasket. It has 2 service's buy a independent garage and the rest buy lexus dealerships and all credit to lexus (Lincoln branch) they are putting a new engine in under the lexus engine warranty without any hassle as I've read horror stories about the head gasket warranty.
I'm very happy that it was plain sailing to get it fixed and I hope to have many days/months/years with trouble free driving this beautiful car.