Jordan Hamilton was the pick, but not for the Mavericks. Dallas and Portland agreed to an exchange, and two picks and two players later, each team got what they wanted.
Rudy Fernandez is a classic case of a player who needs a change of scenery. Love or hate him, and there will be plenty of both, he's certainly had success in the past, and maybe all he needs in a new system with surrounded by players who just won a championship and a coaching staff that was instrumental in getting them there. Fernandez seems likely to replace DeShawn Stevenson or Peja Stojakovic in the rotation; certainly, he is already an early candidate to become the starting shooting guard for the Mavericks, while Jason Terry still gets a lot of minutes there in his sixth man role.
The other player which the Mavericks were able to obtain was Petteri Koponen. He was actually a first round draft pick back in 2007, but has played in Europe since. Last week, Ball Don't Lie had an interesting story on how he felt as if he was being held captive, because the Blazers showed no interest in actually bringing him over, even though he was ready.
If that is indeed the case, it shows that he might not be as much of a throw-in as it might have initially seemed. Koponen has been out of the spotlight since 2007 (when he was drafted), but he was thought of as an NBA prospect then. Four years ago, he was a pass-first point guard who excels in the open court, and had a solid jumper, although lacked the athleticism and overall point guard skills needed. It'll be interesting to see what the Mavericks do with him coming up. With someone this obscure, it's really impossible to tell his situation and how ready he is; however, the Mavericks do have a need at backup point guard, and also have a D-League team where they can keep a closer eye on players. Its very likely we might see more of this young man sooner than later.
Here's a line to Draft Express's page for Koponen. Keep in mind that everything except his stats is quite old. He appears to have put up decent numbers, although there's no telling how competitive the Italian league he was playing in is.