There are three operators of the AN-124 at present, Volga Dneiper of Russia, whose agreement with Heavylift of the UK has terminated, Antonov Design Bureau of the Ukraine and the Air Force of the Russian Federation.
All three use Shannon, the first two regularly (Volga Dneiper has a base here) and the most I've seen on the ground at one time is 4 aircraft. The Russian Air Force visit two or three times a year ferrying trucks to Cuba.
All tend to fly across the Atlantic only as far as Gander as they are severely range restricted when fully laden and fly at around Mach .59!! They are not SELCAL equipped so the radio man has to listen to all the HF static for hours on end.
Take offs, when full, tend to be a slow and laborious affair. There has to be a reasonable gap in traffic before take off as engines have to be run first at 50% for 2 minutes and then at take off power for a further minute before brake release - this causes consternation at many US airports!
When empty, or lightly loaded, the same procedure is followed but take off can be spectacularly fast.
The aircraft carry two internal cranes each capable of lifting 70 metric tonnes. They can kneel to accept cargo and are fully capable of ground operations without hook ups.
Boeing regularly use the Volga Dneiper aircraft for outsize load ferries into Boeing Field.
There is another colour scheme on one of the aircraft in the colours of the defunct Titan Cargo Airways and it operates for Volga Dneiper.
The AN-225, six engined, twin tail version of the 124 has just completed ground tests and is about to fly again after major refurbishment. ADB expect to show it at Paris this year and then put it into service. No doubt it and its half built sister will eventually appear at SNN. I saw the original at Paris in 1979 - big is an understatement.