Formal or Informal?

Which phrase or type of language would you find in a formal letter? Which phrase or type of language would you find in an informal letter?

I am sorry to inform you that...

I am very grateful for...

Why don't we...

I will not be able to attend the...

exaggerated punctuation, such as "That's awesome!!!"

idioms and slang

contracted verb forms like we've, I'm, etc.

Give my regards to...

I look forward to hearing from you...

Let me know as soon as...

The use of emoticons, such as :) ;) :P

Dear Tom,

Dear Ms. Smithers,

Best wishes,

Yours faithfully,

common misspellings, such as "l8tr"

I'm really sorry I...

Unfortunately, we will have to postpone...

polite phrases

Love,