Once you get your SD4 dialed in, I think you'll be quite pleased.
On a horizontal 25mm disk, I have only .03mm of deviation, on a vertical 25mm disk, i have .06mm of deviation. I'm extremely satisfied with the accuracy of gears, auto parts, etc that I print; I don't see a need for me to try for anything beyond that!
This is especially useful when printing things like that NASA wrench that is printed as one single print, moving parts and all, and works right out of the printer. Its a great demonstration of 3D printing capabilities.
This week, I'll try to take some photos of the mods I've found to be helpful.
Edit:
FWIW, I've found ABS easier to work with than PLA when doing set-up and calibration (your results may vary). Not all suppliers of filament are created equal, and some suppliers' quality varies greatly from spool to spool. I got very lucky with my first spool of filament; the second sucked. The only redeeming fact was that I knew my printer had been working well, so I knew it was the filament. If I'd have got the second spool first, I would have probably given up on my SD4...not the printer's fault. With the supplier I use now, I don't even have to measure and adjust extrusion rates between spools.