And here it is! The moment we've all been waiting for:
$ dmesg
OpenBSD 4.1-current
pxammc0 at pxaip0: MMC/SD/SDIO controller
sdmmc0 at pxammc0
scsibus0 at sdmmc0: 2 targets
sd0 at scsibus0 targ 1 lun 0: <SD/MMC, Drive #01, > SCSI2 0/direct fixed
sd0: 14MB, 14 cyl, 64 head, 32 sec, 512 bytes/sec, 29120 sec total
Now OpenBSD based Z's can utilize the on board sd slot!