In anticipation of the 645D I first bought the *istD, then the K10D, the K20D and now the K-7....
Okay, seriously: I picked up an 645AF 150/2.8 this winter, but not actually in anticipation of the 645D. I love to use the 645 optics on K-mount for macro. the 645A 120/4 is nice for up to 1:1. For 4:1 magnification I have stacked the 645A* 300/4 with the 645AF 75/2.8. The 150mm stacked with the 75mm gives awesome results at 2:1, and sort of fills the gap.
Would love to get my hands on a 645 bellows too.