I decided to send a letter to all my Facebook friends on their birthday, and to ask for one in reply on my birthday. If they were more like an acquaintance or somebody I wouldn't want to spend time writing to, I de-friended them.
I did well the first year, then the second year only my friends with birthdays before April got a letter. Last year, I only sent one to a friend, who's birthday was in January, when my 'resolution' energy was still high.
I didn't count on my laziness or procrastination :-(
I will endeavour to get back into it, though, as my friends seemed to appreciate getting a real letter, even if it is only once a year :-)