I've been able to keep up a 2:1 win ratio. Because I'm still in the practice league (18 games left, so I've played 32), I expand fast. I can barely defend the enemy's first attack, after which I quickly build a superior army.
Usually 1/3 Zealot, 1/3 Stalker, 1/3 Immortal/Colossus/Other. Depends on what the enemy's using of course.
I'm afraid I'm addicted.
Oh and the people who are afraid to play online have no idea what it's like.