Quote Originally Posted by Layne
I agree with barmaley, I don't find esl learners mistakes nearly as irritating as native speakers.
I agree with you, I'm indulgent toward foreign learners mistakes too. It's always nice that a person made at least that ammount of efforts to learn other langiage.

But there is opportunity that my enthusiasm will fade a little if the person speaks with a very strong accent and uses wrong stresses all the time turning every his/her word in an enigma.
Though I'm always admire those who mastered cases, that's my weakness. I usually think to myself that person speaks Russian "(almost) perfect" even if he/she has a poor vocabulary or/and strong accent.
So: cases are good, strong accent is... not so good.

Can you tell what mistakes of esl learners are more irritating than the others? Or what aspect of the language (word usage, articles, etc.) is more important for making an impression of "perfect english"?