Dutch also has a formal (U) and informal (je/jij) version for you...
And dot my i's and j's for pretty much the same reason as J.Allen.
No, I think that's not what I meant.
When you're writing a letter, or address anybody specifically in a written form, you're supposed to capitalise the pronoun even if it's a friendly letter between close acquaintances - "Du" just like "Sie".
It's just that those conventions aren't taken very seriously anymore in informal letters (e-mail specifically, or online message boards).