Sadly, it seems as if the Sony PlayStation 3 won't be fully backwards compatible. As reported in The Age today:
...the PS3 might not play background music to the popular "Tekken 5" combat game, and some scenes from the "Gran Turismo" racing game might freeze, according to Sony. The game "Suikoden III" can't read data from a first-generation PlayStation, while a virtual gun in one of the "Biohazard" games won't fire properly.
Some older games won't run on the PS3 at all...
We can only hope that these issues are corrected some time in the future with updates.
Also, it's not really related but the Japanese launch weekend numbers are in now...
60GB version: 45,774
20GB version: 35,865
Ridge Racer 7 - 21,654
Gundam Target in Sight - 21,309
Resistance - 13,545
Genji - 8,766
Sega Golf Club - 1,410
And the rumour is that there will only be 30k shipped out at the end of the week as opposed to the 100k reported.