Crazy, man, i was in France, Ireland and England over Xmas and NYE last year!
I was in London for Christmas, which was really beautiful, except for the fact that nothing runs on Christmas day, meaning you have to walk everywhere. Christmas Eve was pretty nice, though. Boxing Day (the 26th) everything opens back up as it's a huge shopping day, but in Ireland it's St. Stephen's Day, where just about everything is closed until the evening...
As for New Year's Eve, I spent it in Paris, which was a BLAST. I highly recommend it. Most visitors party it up under the Eiffel Tower, which is cool, but it's far from anything to do afterward, and getting on the metro just after midnight is madness - I'd recommend hitting up the Champs Elysées, or better yet, the end of it at Place de la Concorde, which is closer to all the after-parties going on. Personally, I started out in the St Michel/St Germain area and had a wicked time, then moved over to Concorde for midnight, then went and partied it up in the Bastille. All of it's within a mile or so radius, which made walking around to all the events easy... the only tough part was scoring a bottle of Champagne that night, so shop early!