I was talking to a fellow windie this week and he told me he had spent two nights posting christmas cards to all his custies.
Thats nice of you I said,
Its amazing what a difference it makes to tips, says he. 
I was considering posting them myself to wish customers a merry christmas, but don't want customers to feel obliged to give tips...
What would you think if YOUR windie sent you a card? I'd feel awkward and think they were after a tip. Next chance I have, I'd change windies. Only my opinion, and everyone sees things their way I suupose. I've never done this in over 20 years.
I've found that when I forst started, I was a lot cheaper than I work for now and got a lot of tips. Now my prices are higher, I get less tips. Dunno if that tells me anything, but a tip is a tip, if I get one, good, if not, so what?