The amazing CHDK: http://chdk.wikia.com/wiki/CHDK_in_Brief for those who aren't aware of it. If I could ensure a new camera was supported, that alone would be enough to make me buy it over any competing models.
[1] - http://magiclantern.wikia.com/wiki/Magic_Lantern_Firmware_Wi...
Unrelated: Trammell Hudson, the guy who started Magic Lantern has done a lot of other interesting stuff - such as open source helicopter control software.