hmm i alt tab out all the time and have no issues.
it does take about 30-45 seconds for graphics to load back up and i get a fps drop when tabbing back in.
course I'm on a laptop with onboard video but i have 8 gigs of memory and an I5 processor so that might make it a bit easier on me.
heck this laptop runs AH2 smoother than my old desk top did in 2007
and i had a 300$ vid card in it.
what's great is being able to play aces high while watching netflix hulu or listening to music. never could do that on my old pc.