My Pandora started out as being able to run for about 8 hours when I first got it, if I didn't turn it off or go into low power mode. Now, thanks to Notaz's work around the 1.73 release, it currently runs for about 22 hours (although part of that is me being more anal about turning everything off; wifi, USB host, TV out etc., letting the system turn off the 5v out). So it depends an awful lot on what you're doing exactly, and quite a lot on optimisations of the kernel which won't be ready at launch.
I'd also trust numbers given by the community more than those from the manufacturer, however well intentioned the manufacturer is, after Pandora claims were a bit unbelievable for a good few years.