My 2.4GHz one is about to run out after 4.5 hours running Safari, iTunes, Mail, NetNewsWire and I've played a couple of 720p TV Shows and watched a fair bit of YouTube. Display at full brightness, volume at max.
I'm calibrating it right now - seems to be the same as my BlackBook but watching the HD shows put much less of a strain on the system on this machine than the old one.
Just waiting for it to turn off so I can plug it in and get the battery back to full.
So far I've been seeing near-enough results to the 5hr claimed life.
Same mode as you right now - unplugged, screen brightness full, volume not at max, and in fact, far, far less GPU-intensive usage with mostly Entourage and Firefox, plus a pretty low-impact VPN tunnel.
And it's down to 39% after one and a half hours. And I know all my batteries have the same runtime.
I call fer-laaaaming, humongous, BS.