Dunno about December but we went at the end of February and I don't think I've ever been as cold!! But with the snow it looked beautiful, but then I am a girl so I like that sort of thing!!
Well I'm going with a girl, so at least she'll be happy. I went in July last year and it was 38C. I don't expect it'll be that warm nearer Christmas.
Went start of Feb this year... If anything it was slightly warmer than in England at the time, though it started to snow a little on the day we went home. I would say it adds to the romance if it's cold and snowy Look out for the shop selling Russian dolls of BFC players near Charles Bridge, superb stuff!