Extrapolating from the datasheet and applying to the power supplied by Pandora, I get: SPL: 91dB, 0.2W/0.1M, 1Khz
The speakers aren't crazy loud, but are fairly strong. I tried a number of speakers to find one that provided a rather flat frequency response curve and a lower resonant frequency. I was hoping to get a sound that wasn't too 'tinny' and had enough midbass to make guitar notes sound full. The speakers we are using fit the bill, but they are still just tiny little speakers so its not going to be a mind blowing experience or anything.
When I am testing things, I tend to listen to music with the volume all the way up. Some louder songs are a bit much for me, but most music is fairly comfortable. The sound of reloading a gun in Quake is a little sharp and loud enough that I back the volume down a bit. Overall, I wouldn't plan on using the speakers on a noisy bus or anything like that. The volume is comparable to my PSP-1000, DS lite and even the GP2X F-100 I have here. The volume is no where near as loud as the iPhone when you have your hand cupped around the speaker hole in the right way (which amplifies the sound greatly) but that's what a million dollars of engineering resources will get you.