Sideways may qualify as a "Romantic Comedy"- but if looking for a date movie, I would vote "against".
Honestly, the first time I watched it I was on a date, and she got REALLY aggitated about the whole cheating before your wedding, and lying to the woman you are interested in angles of the plot...
I would say she was just over sensitive, but most women that have said anything about the movie say the same things- "What? that movie about the scumbag that cheats on his fiancee with that girl from Grey's Anatomy?- that movie (expletive) sucks".
I'm usually only in the mood for movies like this around the holidays and so I agree with this pick and would also add Family Man with Nick Cage to the list. My wife and I watch Family Man every Christmas eve after Santa has come before we go to bed.