The handshake thing worries me a bit... that seems more in the category of things that many people rely on, but actually tell you very little about the person.
Someone with a good handshake either:
* just naturally learned to shake hands in the way you like
* found out that handshakes are important to first impressions and spent time perfecting theirs (including maybe a handwarmer in the pocket...).
Does either of those things reveal any important traits?
People naturally have different levels of perspiration & circulation in their hands, particularly when nervous. Anyone going for a job interview they care about should be at least moderately nervous.
So someone might have a cold clammy handshake purely through genetics. How many strikes against them should that be? Firmness and eye contact are based on habits, generally -- again, the developer who's thinking ahead to the "important" parts of the interview will just give you the handshake they learned as a child. How many points against them should it be if it's very soft (because they were raised by an arthritic grandmother)?
Too much rambling for a small point, but I just want to say you should try to reserve judgment on exactly this kind of thing until they've had a chance to relax a bit, get talking, etc..
Personally, my handshake is probably pretty good, but I'm not going to be really at ease talking with you until we've been interacting for at least a few months. I've learned to fake it over the years (and keep calm enough in the face of strangers that I can think straight, for the most part...), but the hiring process is definitely harder on introverts.
I went through an phone interview a few months ago that included some quizzes, talking through solutions to invented problems, etc., and was glad she agreed I could hang up the phone while I thought (and took notes)... this resulted in a much better answer than I would have given if forced to think through it while on the phone with a stranger.