How good or bad would chainsaw bar lubricant be as a bicycle chain lube? A former coworker asked me this today, and I don't have a good answer.  He has access to plentiful quantities of chainsaw bar lubricant, the stuff that helps a chainsaw's chain move around the metal support poking out the front of a chainsaw.

Bar lube is primarily intended to decrease friction between a non-moving metal surface and the backside of a cutting chain.  Secondary effects are lubing the chain and helping to transfer heat away from the chain to the bar.

Its got to be better than CRC or WD40, but would bar lube be just simply worse than proper chain lubricants, or a lot worse?

Personally I'd just use proper bike chain lube. The question is specifically about chainsaw bar lube.
On a chainsaw is it called bar lube (not chain lube).
It is designed to lube the bar.  

This is chainsaw chain:

Not the same beast as bicycle chain. 
I don't even think there are rollers. 
Bar lube is more viscous than bicycle chain lube. 
Bar lube does not need a long life - it is going to get thrown off. 
There is an excess of bar lube and big gaps compared to a bicycle chain. 
The chain itself only needs to last longer than the cutting teeth.

Yes they are both chains but that is about all they have in common. 
It is a bar lube.

I would chose 3 in 1, motor oil, or transmission fluid over bar lube.
Yes I would use bar lube on my bicycle chain if I had nothing else in the shop but I would not use it just because it was free. I would even use WD 40 for a single ride and get chain lube the next day. Not a great lubricant but WD 40 would not gunk up the chain.

You pay $20+ for a decent chain. Why would you skimp using a product not designed to protect the chain? A good chain lube is not very expensive and goes a long way.