Then, in First Contact we find out that Data can turn it off at will. Gee, no more having to learn how to deal with your emotions in high-stress situations! Isn't that convenient? Then, in Insurrection, we find out that the chip can be popped out and left in his sock drawer. So much for emotions being a permanent part of Data's life. And in Nemesis, well, they didn't even bother addressing it. The movies really did a lot of damage to Data's character, despite him being a heavy focus of all four stories.
I'll admit, although i personally liked the emotion chip storyline, i
hated the 'turn off and on at will' cop-out they brought in for First Contact. I also agree that not even mentioning his emotion chip, let alone him seemingly not having
any emotion chip at all in Nemesis was lazy writing, i suspect Brent Spiner had a hand in that, since he probably wasn't a fan of the emotion chip angle, though i'm just guessing. I'm sure there was a novel that explained it, although i can't remember for certain.