Freecycle is only as good as the moderators.
Ours have limited the wanted posts.
Its always worth asking if you havnt seen what you want recently.
But its always a good idea to offer stuff as well as receive.
Yeah I try and offer stuff as well as I have things to give, it also gives a better impression to your name.
I don't think ours are limited but people would just hate you if you always asked for things. You would probably get a warning then a banning if you continued though 
Mowcius