For me, I get a lot of freezes when it is summoning creatures. It animates the "swirly pillar" and then never finishes summoning the unit, leaving the pillar swirling forever and I can't take any actions that will advance the game (even surrender), only hover and magnifying works. Have to close Scrolls to get out of it.
It used to do this a lot a few patches ago but then it was fixed, seems to be back again in 0.82 though.