The range of occupations expecting a tip is expanding. Letter carriers, personal trainers, dog walkers, housecleaners, doormen, small city mayors, and school teachers are all listed in a guide on who to tip and how much.
I would think the doorman at one of those ritzy Fifth Avenue addressses must pull in some cash this time of year and who wants a dirty look all year every time you come home.
If you have the means and the service is good, there's nothing wrong with a gift, but with some occupations it seems awkward, but it shouldn't. What's wrong with handing an underpaid local reporter a $20 for the job they do ?
Holiday Tipping Guide for 2012 - How Much to Tip For the Holidays