I don't know too much about Rep. Kirsten Gillibrand, New York Governor Paterson's choice for Hillary Clinton's old Senate seat, but from what I've read this morning, she's pretty conservative as Democrats go. She has a 100% rating from the NRA, she supported telecom immunity, she used to work for Al D'Amato, etc. She's had some pretty anti-gay stances, too, but has demonstrated some recent flexibility on that issue.
Now, all this might be justifiable if she were being appointed to a Senate seat in, say, Colorado, where a moderate voting record would be really helpful in the next statewide election. But she'll be running in New York, where liberals like, say, Chuck Schumer and Hillary Clinton can win statewide. Meanwhile, elevating her to the Senate means opening up a moderate district to a special election which could easily go the Republicans' way.