I have run across the random zomg knife hack. but it's usually not that bad if you play on servers that has admins.
I'm actually more annoyed at how broken the friends list is than random people cheating. Origin simply is terrible, and battlelog is only an extension of that terrible. A unified friends list is a double edged sword, and probably not the best solution but it's better than what's going on right now.
Honestly, Origin / BattleLog and the game crashing about every 3-4 matches is taking more out of the game than the occasional cheater. I probably wont play the next battlefield unless this stuff changes. (Unlikely.)