Eighty dollars. That's the number (at least for Vista Home Premium) according to this comparison from Coding Horror of the price delta between identical Dell systems configured with Vista and Ubuntu Linux.
The hardware is essentially identical. We can infer that Dell's price for a Windows Vista Home Premium license is $80. An OEM copy of Home Premium runs about $129, so it's cheaper to buy the license from Dell than it is to buy one yourself. But if you have no intention of running Windows, you just saved eighty bucks.
Kudos to Dell for doing the right thing and ending the Microsoft Tax. It's also quite possible today will be looked back on as an important turning point in the history of desktop computing.
Do you think so? Between unbundling their PCs from Windows and announcing they'll be selling PCs retail through Wal-Mart, it's definitely a turning point in the history of Dell. The whole "history of desktop computing" thing remains to be seen. Ask me again when a second major OEM announces they're following Dell's lead.
Oh yeah... almost forgot. So does a Dell box running Ubuntu avoid the latest Dell-Google "evil" plan to make money off our inability to spell?
Update: Ars Technica says the tax is $50.00 (at least on the high-end XPS system).