There's been a lot of comments lately regarding Deng&Gordon and the Qualifying Offer without realizing how poor an option that is for both sides.
First of all, it makes the player believe he's not coming back, and the team treating the player like they're not coming back. Maybe it's a self-fufilling prophecy, but it's borne out that they don't come back. (thanks to paxson43 in the comments)
Follow that link: since 2000, there's only been 4 players coming off their rookie-scale contracts that signed the QO. That's 4 out of 124 eligible draftees. All of them (with Pietrus signing yesterday) wound up on other teams, and only (in the case of Radmanovic) was the team able to deal the player in that season for something (Chris Wilcox).
And it's hard to deal a player under the QO because: " if the player is playing under a one-year contract and will have Larry Bird or Early Bird rights at the end of the contract, he can't be traded without his consent. If consent is granted and the player is traded, then he loses his Larry Bird or Early Bird rights, and enters free agency as a Non-Bird free agent."
The Bird rights are basically a team's ability to go over the salary cap to sign their own free agents. With the way the capped-out NBA is, that's the only way for many of these players to get above the mid-level, either with their own team or through sign/trade.
So, just a reminder when bringing it up: the QO is really a last-resort option, and pretty much a failure in negotiation.