Sony Computer Entertainment America has launched a search engine which lists older PlayStation games and the known compatibility issues. Add to this that the PS3 v1.92 firmware update which also fixed some backwards compatibility issues (PlayStation 2 games only) and the result is a pretty good picture.
However, not everything is sunny and the “fine print” principle still applies. There is a black cloud still covering the area inhabited by peripheral-based games and Sony puts it like this:
"We are working with game publishers and peripheral manufacturers to develop the appropriate hardware to play peripheral-dedicated PS1 and PS2 games on the PS3. Ultimately, however, it will be up to those companies to decide if they want to produce these peripherals to support this gameplay option.”
Let’s be realistic for a moment: how many manufacturers would be inclined to spend more money in developing such hardware, especially since the demand in unlikely to justify the costs. Or to cover them, for that matter. There might be a several isolated cases, but not much more.