I found some interesting words about accent at http://china232.com/blog/2007/07/:
"The mistakes almost sound natural. It’s the same story with pronunciation. This is just called an accent. We hear them all the time and it’s very easy for us to understand."
"natural mistakes" -> :-)

I have been told that my accent (English Geordie) is hard to understand. I had a real hard time when I moved to Canada, people were constantly telling to slow down and repeat my self. Now after 6 years of living here I have a Mutt accent!!!

For me I find the Newfoundland and Bretton accents of Canada difficult to understand especially when they have had a few whiskeys!

I think it's all about exposure. I have no exposure to maritime Canadian accents and when I meet someone from the other side of the country it usually takes a little while to adjust to hearing them. That being said, I am surrounded by non-native English speakers from Asian countries and I have no problem understanding them at all, but they often complain of being completely unintelligible when they go travelling to the states.

My friend from Malaysia is fluent in English, but he grew up in a boarding school in the UK, then moved here. It's almost impossible for people who don't know him to understand what he's saying, because he talks very quickly, but also because he uses British English with a Malaysian accent!

There are no "mistakes" really, especially if an entire group of people are making the same "mistakes", it just becomes a new speech variety for that language.

As a native English speaker, I find the Indian accent extremely difficult, but of course with every accent there’s people you can easily understand and others you can’t, it really depends on elocution and speed.

I find too that it really only depends on exposure.

i think it'll be difficult understand http://www.youtube.com/watch?v=Nx5k7jKGQyU
:-))))
And don't ask me - is this russian accent.
When i heard this i laughed as a child.

@gsold

:-)))) I thought he spoke Russian at first.

Both me and skyblueteapot think American English is usally the hardest to understand ;-D

While nobody would think that Vitalij is a native English speaker, I have no problems understanding him. It's not uncommon at all for people (regardless of nationality) to have a thick accent like that.