Got a HP PSC 2179 here, and am still on the original cartridges nearly a year after buying it. They're £35 a shot, yes, but so long as you don't use "best" for everything "Normal" is my usual setting (with Best, Good, Normal, FastDraft" being the choices avaialble to me. Fastdraft uses next to no ink, and is *stupidly* fast (read: 4-7 seconds for a full page of text), but the quality's pretty poor - but fine for printing datasheets of tech articles for reading (I prefer to read stuff on paper rather than on screen - I do recycle though!).
I won't be bothering to refill these ones, as they last so long. I'll just make sure that I get the high volume versions of the cartridges.
My old HP DeskJet 890C, which died recently due to a paper feed problem (I got it free like four years ago!), did get refilled, and used a lot. The cartridges in that were great, if your normal cartridge was like a car's fuel tank, the 890C would have been the van with the entire back being a fuel tank like the one in the old Gumball Rally movie. Those things were huge, and lasted forever.
Best printers for refills are probably Epsons though, as they still don't have the printheads built into the cartridges, so your cartridge isn't going to die after being refilled a couple of times. I wouldn't really want one though for that reason - if your print heads die, new printer time. Whereas with a HP or similar if you have head problems, just dump the cartridge.
Refills: Do they work? Yes, if you follow the instructions.
Are they worth it: If you do a lot of printing, yes. Or if you have a greedy printer.
...just whatever you do, wear gloves. That stuff is a PAIN to get off your hands.