I have played various recent multi-platform games, like Call of Duty: World at War, Resident Evil 5 and Far Cry 2, I don't notice bad PS3 performance (although not measuring up to Killzone 2 and Uncharted in terms of graphics). I don't think such games truly provide much different experiences on either 360 or PS3. I think people exaggerate a lot (maybe there are tiny advantages, but I think you would have to run them side by side and still ....).
Other games which required a harddrive install on the PS3, also demonstrated clear and obvious loading improvement, such as in Oblivion.