Probably not too much but it depends on the context. If you're cussing up a storm b/c you'e ranting, I don't think Youtube will think too much of it. If you're cursing while talking religion, politics etc then it could get flagged.
however, with the new rules and regulations, more advertisers are shying away from anything even remotely controversial and that includes some swearing so although your video may not get flagged, it could be deemed not "advertiser friendly" and you won't be able to monetize that specific video.