Is Taylor on for season 4??

Taylor will probably be in season 4 it's not like they can get rid of her I think that Nate and Serena will get together and Vanessa and Dan will get together. In the commercial I saw for the second part of season 3, Taylor kisses the guy who sells people drugs.

Not that I know of.

actually, now that you mention it, when she was talking about haiti she said that she was 'focusing on finishing the LAST season of gossip girl' and there is going to b 4 seasons, do maybe, i dunno...

I read on a fan site that she'd be on & off the show to work on her band

Not at the first few episodes.
According to this source:link
"She's been looking for trouble all season long, and it looks like Jenny Humphrey is going to find it - when Gossip Girl returns next season, she won't be there.
A source close to the CW soap tells EW that Taylor Momsen's character will be absent for an unspecified number of episodes at the star of the fourth season.
Why? The vague "creative reasons."
“When you watch the season finale,” the insider adds, referring to the current season, “you will see that we’re doing something very big with her character.”"

Bella, I was listening to my favourite radio station the other day (maybe two days ago?) and they announced that Taylor quit GG after a bust-up with the producers.

Now, I don't know how legit this source is, but it's one of the most popular stations around (Nova 96.9), and I'm pretty sure they'd do their research before telling God-knows-how-many-listeners about something they're not even sure of.

I don't really know, but we definitely won't be seeing Taylor in the first few episodes of season four.