In the face of ultra-thin MacBook rumors, Think Secret claims that a modest processor bump for the MacBook will be the only hardware refresh for the rest of the year. Keep in mind, however, that Think Secret only says there won't be any more hardware updates. They don't say anything about new hardware announcements. Still, a MacBook speed upgrade seems odd since Apple doesn't like to mix processor speeds between consumer and pro lines.
With the MacBook already topping out at 2.16 GHz (which is only 40 MHz slower than the low-end 2.2 GHz MacBook Pro), an update could cause some confusion. Especially if it includes a switch to the Santa Rosa chipset. So could there be a MacBook/Pro/Slim (arrange those as you see fit) still in the cards or even a Mac Mini successor? [Think Secret]