From Salon (sub. req. or ad click-through):
"Your inkjet printer is probably lying to you. According to the research firm TÜV Rheinland, printers routinely report that their ink cartridges are empty when they really aren't. The study was commissioned by Epson, whose printers -- coincidence? -- were found to be the most honest. When Epson printers reported they were empty, they were actually only 80 percent empty. This isn't at all very honest -- imagine if the gas pump charged you for a full tank after filling up just four-fifths -- but it's a fair amount better than Kodak's EasyShare 5300 printer, which reported being empty after using just 36 percent of its ink. That is, the cartridge was almost two-thirds full when the printer recommended buying a new one."
Inkjet printers are such a scam. My color inkjet printer sits unused because I can't bother to refill all 6 of the cartridges. And you can't just refill the black cartridge; the printer will actually refuse to print unless all six cartridges are full. This explains why printers are so cheap to buy nowadays. They're following the disposable razor marketing formula.