Well, after reading all of the replies here I guess I'm in the minority. First of all let me say that I was also totally against using generic inkjet (or any other) cartridges for all of the reasons outlined by other posters. That is, until 3 years ago. I happened to open what, today, would be called a spam email from a 3rd party supplier of inkjet cartridges and because I was desperate for a cartridge for an older Epson (Stylus Photo 740) I decided to order some from these guys. They shipped direct to my door (I'm in Canada) and only charged a modest freight fee. I used every single cartridge over the next few months and never had a single issue...no clogging, no leaking, no apparent difference in colors.
So when it came time to order cartridges for some of our other printers (Epson 440, 800, 850, 777i, CX5200) I cautiously made purchases of inks until I was sure that there were no problems. Each purchase was made to be over $50 USD, which is their minimum for FREE shipping. To date I have ordered at least 10 times. Always free shipping, always ships direct to my home, never once made a mistake in either type or quantity of cartridge or price, always arrives in less than a week.
And, of course, the reason I switched to generic in the first place was price. The second time I ordered I got 12 cartridges; 6 Black and 6 color for my 740. I paid $42.86 USD (I bumped it up with something else to make the $50) which averages out to $3.57 per cartridge. Since then prices have gone up a bit and I'm using different printers. The last time I ordered for my 777i I paid about $6.95 per cartridge. In Canada I have to pay anywhere from $20 to $35 USD for the Epson branded ones.
Now, I'm not refuting what anyone has said here before. It may be that I've just been lucky or that I've only been dealing with Epsons' cartridges. I can't recall whether I've purchased ink for other brands from these 3rd party suppliers. I just thought you'd like to hear some experience from the other side.
My experience in the industry is fairly extensive. I'm a Mac and Windows expert and have been for over 20 years.