I must admit that they are not very good jokes and also that they seam to be connected to another condition where words you hear get jumbled up not dyslexia. I'd also like to take issue with the statment made by Mark;

"Contrary to popular belief, having dyslexia doesn't mean that you can't spell or that you write words or letters backwards. It means that you have significant difficulty learning to read."

Actually that is exactly why I am classified as dyslexic! I had a hugely advanced reading age before I even got into school. My only problem is a tendancy for my eyes to try to read the whole page at once insted of individual lines. I was reading books for 8 year olds alone by the age of 5.
That is why it was never diagnosed till I got into university, people thought that I MUST be able to spell and I was just being lazy.
I can't spell (or indeed type, do mathmatics, read/play music and don't even TALK about punctuation!) and If I have only seen a word written down I tend to pronounce it wrong if it's more than three syllables long.
A classic dyslexic in fact!