Trusted Reviews has a big investigation on inkjet printers and inkjet ink, and their year-long study comparing fading between more expensive manufacturer brand vs. the cheaper crappy brand shows that you get what you pay for. Over three months, the differences between the two were negligible, with pages only fading slightly (but noticeably) in quality.
When you got to twelve months, you got somewhere between considerable fade and severe fade, which makes the page no longer usable. The lesson here is that if you're printing out movie tickets for tonight, cheap ink is fine. If you're printing out photos from your trip to Japan, go for quality. [Trusted Reviews via Crunchgear]