I don't know about other players but I'm using courier very often
to send mana and healing potions as well as refilling bottle.
Its a great advantage cause you can stay in fight with no loss on experience and creeps.
I often play with a friend of maine and he also using it often. For just us two - courier is busy most of the time, so I'm not sharing it with noone else.
If I'm playing public game alone, I often say at beginning:
"I can give share if someone make bird".
Usually I get response:
"I'll make bird" so I'm giving share to him.
If noone responds I'm saying: "just don't ask later".
I'm loosing 200 gold at beginning so I have poor start items,
later I'm making bird ASAP and people
DEMAND share!
Is my name Santa Klaus?
I do understand that in professional Dota games like the ones played on
www.gosugamers.net/dota there is a rule
that one (support) person buy chicken, bird, wards and give share to whole team. On playdota.eu however it is not the case.
I've lost count of how many times my courier died cause someone send him under enemy tower or heroes.
But the worst of all things is that people control your hero! Its happening to me that often that it's almost ridiculous!
And I'm sharing it only with one person... Can't imagine sharing it with whole team.
I get vote kicked few times for not sharing the bird! sick!

If I make a courier it is only My decision whether I want to share it or not.
But greedy players demand it for free even at late stage of the game when 200 gold is practically no money.