There are plenty of achievements and portraits to be unlocked in StarCraft 2, and there were some people that felt the need to make the game un-enjoyable for plenty by farming for portraits and disrupting the ladder. Blizzard is taking a stand against those who have done it, or will.
Blizzard posted over on their forums with this statement directed at anyone who feels the need to farm for portraits.
“This is a warning that the practice of purposefully losing games and/or automating gameplay can be met with suspension from the game, revoking of achievements and portraits earned, or permanent closure of the account. If you're found to be automating your gameplay and/or purposefully losing games or win trading, your account will come under scrutiny, and any of the aforementioned actions may be taken.”
Short, simple and to the point. So if you were thinking about farming in a way that is stated above you may want to think again.
Edit : As per request, unknown portraits that currently cannot be obtained:
(I believe two in the middle row are via collectors editions, but I cannot remember)
Links
us.battle.net - Blue post