On Hagara the Stormbinder, when the Iceshards starts rotating around the room, Ice Block works & as they are coming towards you, Blink will make you avoid being hit.
Invisibility did not work to dodge any mechanic on that encounter afaik.
I tend to keep Ice Block aswell, if an Ice Tomb is about to form on me, I just pop IB while it's still in the air, when it's falling down, it's too late & atleast this way you can tell your raid to focus the other crystal first or just stay alive longer as you won't take damage untill it runs out. Obvious but still worth mentioning I believe.
In addition to this, on Heroic Hagara in the Frozen Tempest phase when you get the "Frostflake" debuff on you, you can dispel it yourself with iceblock but it will still leave the patch of ice on the floor, so you still have to run out of the group off on the side before doing so. This is useful if your healer isn't dispelling you fast enough or can't dispel you.
And on the lightning phase, after the add dies you can still act as a conductor for the lightning (as in it will pass from the person in front of you, to you, to the person behind you) with iceblock up. In 25 man mode they kill the add on me and since I get hit by the lightning much more than other players, it helps a lot with survivability.