Charlie Villanueva, Pistons' eighth pick in 2011 draft For James Johnson and trade exception
Detroit's logic: Joe Dumars made a mistake when he signed Charlie Villanueva and Ben Gordon to large contracts in 2009. Unfortunately the only way he can undo those mistakes is to give up valuable resources to rid the roster of these players.
Charlie-V is one player who could be moved. His situation clearly didn't work out very well and even though Tayshaun Prince is leaving, I'm sure the Piston's will look to move Charlie-V. Giving up their first round pick (eighth overall) isn't likely, as they could net a solid young player, but the Pistons roster has plenty of young talent already on it and keeping Charlie-V could hurt the development of some of these guys (Daye, Summers, Monroe, Jerebko). With this move they'll have cap flexibility and could carefully address their needs moving forward.
Toronto's Logic: I know what you're thinking: Oh my god, no, not the cap space, anything but the cap space!! Realistically though, this would be pretty good for Toronto. The Raptors will probably take a solid but not spectacular star at fifth (Knight, Leonard), but the eighth pick will also hold a very interesting player.
With the eighth pick the Raptors can net a player who will be a gamble, but could possibly be better then our No. 5 selection. If Irving, Williams, Kanter, Knight, and Leonard are taken 1-5, that leaves Valanciunas, Vesely, Walker, and Biyombo left for the Raptors at 8. All three of the mentioned players can become potential stars right away for their teams but hold the risk of succumbing to their flaws early on (size, or transition to the NBA game, not coming over, etc). After having one solid and proven prospect, the Raptors can satisfy their temptation on another risky player, hopefully leading to a steal.
The second part to this is: Charlie-V wasn't always what you see today. He did a healthy 16 ppg in Milwaukee, and in his rookie season with Toronto, he did 13 ppg which was very solid. Charlie-V coming over could possibly be a pleasant surprise.
No matter how he turns out though, this trade will result in choice but to trade either Amir Johnson, Andrea Bargnani or Ed Davis. It will also result in a second-tier Center from free agency rather then a young star (Samuel Dalembert instead of Marc Gasol kind of signing).
Summary: Overall this trade is something which also has little or no chance of happening, but the Pistons will think about it if they don't like what they see on the draft board.