Nope definitely don't. But my mates do. I have a friend here who speaks slowly to any foregin girl he meets. It's just awful. I had to take him aside when he was doing it to my ex Thai Doris. Look, she went to the Thai Oxbridge, then studied an MSc in England, in English, she can speak English! He just can't help it, same as my dad. I've got French cousins, well half French, half English, so they've been brought up in a bilingual household and also studied in England, my dad still talks to them like they are retards.

Not at the start, but sometimes if it's obvious that the meaning is being lost, then I don't see a problem with slowing down as you speak. Just don't be condescending about it, and don't assume the other person is an idiot. They can speak at least one more language than I.

After a lot of years here, I think the most helpful habit a native speaker can acquire is recognizing (and not using whenever possible) idioms, colloquialisms, and complex vocabulary and sentence patterns. This is easier said than done (see, I've just used a little cliche myself) but I've found it makes an immense difference in some situations, and you don't have to slow down your speech that much.

No, but my wife's English is better than my Japanese. Just yesterday she was laughing about a telephone conversation with our daughter at college. Are you losing weight? Daughter: yes, I'm working (at Pizza hut.) Wife: (Assuming she said working out) Lifting weights? Daughter: (Thinking mom said waitress?) No, I'm a cashier... Then they both started laughing once they figured out what each other really said. Cell phones and speaker phones are a deadly combination...