When compared to factory ink (lets say, on my old Epson R200), how reliable is the color reproduction with the typical $50 ebay continuous ink systems? Will the colors fade over time? Primary usage is making prints from an 8mpx DSLR.
Is your current equipment color-calibrated? If not, then third-party ink might be good enough for you. Even if your equipment is calibrated, the money you save by buying ink in bulk may be enough to cover the hassle of recalibrating your printer with each new batch of ink you buy. I bought $100 worth of ink a couple of years ago (refill ink, not a CIS system) and am still using the same batch today.
If you can find a good ink supplier, you will probably be okay, but you should look at actual photography forums for more in-depth information. I've gotten a lot of helpful feedback from Digital Photography Review in the past.
All the photos I printed using third-party ink have held up just fine over the past 7 years. That said, I'm not a professional, I don't sell my prints, and my photos haven't had prolonged exposure to direct sunlight (or, at least, not by my definition of "direct sunlight").
Depending on your situation, you might be better off having a reputable photo lab with better equipment print your pictures instead of printing them yourself and paying premium prices for OEM ink. You could then get the continuous ink system and experiment with your photos yourself, but hire out to do the final prints. If you eventually do have problems with third-party inks clogging up your printer, you will have saved enough money to buy a new printer anyway.
Not reliable at all. Color reproduction is subjective to the quality of the ink itself, and in the case of those continuous ink systems, QC varies by quite a fair bit, and I've have encountered cases where some bottles are diluted by unscrupulous suppliers to earn more money.
Longevity of the print also comes into mind, and those cheap continuous inks do not have technology such as Epson's DuraBrite included. You can expect photos to fade very fast under direct sunlight.
If you are printing photos, and you are serious about your photography, get original.
EDIT: Don't forget - cheap inks might also have a higher tendency to clog up your printer ink heads, resulting in fairly expensive repairs.