My 3GS easily lasts all day through normal use. Normal use for me involves having the Wi-Fi turned on all the time so I can connect to preferred networks (but Bluetooth turned off 'cos I don't use it), sitting on the throne playing Wild West Pinball for half an hour at a time at work, sending about 10-20 texts a day, showing off all the apps I've got to people who can't afford an iPhone, probably a few minutes of calls and the odd bit of web browsing and photo taking. Only really use the iPod functionality when I'm sat round waiting for something.
If I turn Wi-Fi off and turn off the automatic downloading of my GMail, then refrain from poncing around with it all day, I can easily make the battery last 3 days. Not sure how anybody manages more than that though.