I try to send a handmade card, at least once every week or so, to someone I know ...just because. Many of the recipients have told me that it came at "just the right time". I love the ease of email but I love receiving a card or note via snail mail, too.
I always include a hand written personal note inside the card. Most of the time, I write the message on a post it note so that the card is also a gift and can be used by the recipient if she/he wishes.