How to spell "did you"?
I have the impression that some people spell the second 'd' as, well, 'd', but sometimes it changes to a sound like 'gi', so it 'did you' sounds like 'digiu'. What is the correct form?

Hello zymon,
"Did you" is correct. Being from the south I hear the digiu that you are speaking of. It is a running together of words but when slowed down it is, or is supposed to be "Did you"

Yep, Rob is correct. This is real spoken English as opposed to the precision that you learn in the classroom.