My Python answer for the second question, where `post` is patrio11's post as input:

    from  collections import defaultdict
    from string import ascii_letters

    d= collections.defaultdict(int)

    for letter in post:
        d[letter] += 1

    print [letter for letter in sorted(d, key=d.get, reverse=True) if letter in ascii_letters][2]

Any comments on improvement for readability or conciseness?