I TOTALLY applaud the concept, but let me offer another point of view...
I haven't used them because I'm one of those penny-pinchers that itemize everything, so my small amount of consumer "junque" goes to Goodwill or St. Vincent's for the tax deduction, plus, they pick up if I have a big item. (Up to $500 a year, with no itemizing; over that, you need an extra form. Why give away a tax deduction?) Goodwill & St. Vincent's (or any charitable organization) do a good job of dispersing the goods over again, plus turn a profit at it to keep their good works going.
Just more gullible taxpayers/consumers out there, spending money on stuff, tiring of it and then giving it away with no tax hedging whatsoever. To me, that's just money down a rathole, and I DO keep my fiscal house in order so I CAN have the right to b*tch about what government does with our money, LOL! ;)
I am, however, glad to see items getting one or more round of use out of them prior to them going to the landfill. I know, I'm no fun, but thwarting taxes is my hobby, and I don't mind sharing the knowledge with others. :)
As far as taking free items from Freecycle just to donate them for the tax deduction or to sell it? I couldn't morally justify that for myself though sadly, I know of a person who does this. :(