And before anyone tells me "men don't do that sort of thing" can I just say that two of the women I've asked about this have female partners.
I can just about comprehend (in a distant sort of unsympathetic way) the argument that "we've been together a million and one years so his/her rellies are mine so I buy them the presents from both of us"...but Christmas cards to your partner's friends? One of DP's mates' wives sent a card to the Inferiority Complex, addressed and written by her and all, with just his signature, before I'd even met her (and believe me, writing out all our names takes a long time. She'd done it in her best handwriting, too, you could tell). Christmas cards are not exactly fundamental. I'm not sending any at all this year, I reckon.
Come to that, why buy presents on your partner's behalf, anyway?