Don't think there's anything wrong with Downton Abbey on Christmas Day at all - in fact, I think it's a good fit for the ITV audience, a decent contrast to the BBC offering, and will do surprisingly well on the day.
The BBC Christmas Day schedule is solid, if not particularly exciting. I think 2 animated films, followed by an animated short is overload, really - though is preferable to the Shrek The Halls and Jim'll Fix It that got dropped. Ab Fab will be fine at 10pm and I think Michael McIntyre will be better than some expect. It's a late enough slot for that kind of show to work OK.
The BBC's efforts on Christmas Eve and Boxing Day do look an awful lot better than last years, though, which I'm really pleased to see. If anything, Christmas Eve is a little over-stuffed, while The Borrowers adds a bit of oomph to pre-watershed Boxing Day that was entirely lacking last year (Nigel Slater, Countryfile, Antiques Roadshow

).
Actually, it's worth reminding yourself just how utterly awful those two days were last year!
Christmas Eve:
http://www.bbc.co.uk/bbcone/programm...don/2010/12/24
Boxing Day:
http://www.bbc.co.uk/bbcone/programm...don/2010/12/26
The ITV drama swap of Fast Freddie and Poirot makes lots of sense to me. The latter would have had a very large crossover with Great Expectations.