U.N. What do the worlds armed services think?

this is a question that popped into my head last night as i was watching the news..
what do the armed services of the world think of the U.N.?
as far as i know all countries signed in to the U.N. have to supply troops in some capacity or other..is this correct?
if so..what do all the services think of this..is it some sort of punishment(you have been a naughty boy and its off to the U.N and some time in sudan etc)?.
or is it some sort of R+R(whoo hoo a purple heart and and a holiday in haiti etc)?.
i ask this question because it seems to me that the U.N has no authority/power..i have even heard that in some cases they are not allowed to use live ammo?
if that is true i would not like to be assigned to the U.N as a soldier