While it's unfortunate to still have to be writing this in 2012, when most games have their multiplatform houses in order, it seems that the PS3 version of Mass Effect 3 has a lot of trouble sticking to its assigned 30 frames-per-second.
As a video on Eurogamer shows, while both game suffer from slowdown when things start exploding, the PS3 version frequently drops quite a bit lower, and will also drag for longer in outdoor sections, often hovering around the 20 fps mark.
It's disappointing that one of the year's biggest games, in a year most other multiplatform games will be largely identical on both consoles, quite literally lags so far behind on PS3.
Mass Effect 3: PS3 frame-rate issues persist in final game [Eurogamer]