Hah, you used the 16x18 Sara I had Redshrikes make. Glad it was useful to you! Here's a link to the spritesheet in case anyone wants it:

http://opengameart.org/content/sara-16x18

Everything you said for the first 8 minutes or so I felt like you were preaching to the choir.  I wholeheartedly agree with it.  All of it excellent advice, things I've said myself more than once and all stuff any good artist should know and follow.  That isn't to say that the rest isn't a great tutorial ('cause it is) but it's a bit different when every other word makes you want to point at the screen and say "Yes!  Exactly!  He gets it, why doesn't everyone else?!"

For references I would like to emphasize that real world references are better than pixel art ones.  Other art is a good way to learn techniques but it's also extremely easy to copy mistakes or repeat things that were made to work within a restriction you don't have.  Real world references are always better.  The way I tend to work is either only with real world references or with with both pixel and photo references.  I almost never work with just a pixel reference and in the very rare cases where I do it's for something I have already reciently and heavily researched.

I think it's really cool that you built multiple examples for different skill levels using different methods.  Great idea, I'd love to see that concept expanded on somehow.

I think it's important to point out that while it is possible to get a good result by starting with an outline most professional pixel artists do something similar to Bart's second method, where the shading and volume is done first.  Usually the sillouette is cleaned up a little later in the process.  It's a great way to define volume and light so that the end result has more dimention with good contrast.  The extranious bits are carved away and the outlines (if there are any) are added at the end with the other details.  This also means that on things with more complex shapes there is less tweaking and redrawing.  It tends to be a faster way to work.

Actually blocking out the shading on the reference image is an interesting method.  It should be really helpful to a lot of people.  If you're not going to be precise in your blocking please be careful not to introduce and recreate errors in your final image.  In your example there were a few problems with this, like a subtle curve up again with the shadows on the left side and a little zigzag in the shadows of the neck of the vase that were both lost.  I'd suggest turning that redline on and off as you work to avoid that problem.

This is a good tutorial, I hope people find it useful!

Your delivery is very clear and easy to follow. I found this helpful, thank you.

I've been looking for something like this for a while now. Nice one Bart!