Thanks, porchapples! Also, there are numerous comments from home cooks on Williams-Sonoma's website (WS first sold the KA extruder) and now on Amazon, as well. Their experiences of what worked dough-wise and what didn't might be helpful.

I am also going to check out Cooking By Hand, by Paul Bertolli, because I have heard that it contains a discussion of homemade macaroni.

http://www.guardian.co.uk/lifeandstyle/wordofmouth/2010/aug/26/how-to-make-perfect-pasta
This is the link to the guardian article.

Hi porchapples! Good question -- I have the KA extruder attachment but haven't used it yet so I look forward to our fellow foodpicklers' answers. Meantime, could you please post a link to the Guardian UK discussion you mentioned?

While KitchenAid does make an extruder attachment it's made from plastic (as opposed to metal dies) so it creates the shape but doesn't add texture. My standard pasta dough is egg and all purpose flour mixed on a board. No olive oil. But 00 is absolutely fine for pastas. No reason to adapt your dough for flat vs extruded pastas. For filled pastas you do have to adjust thickness of sheets as needed.

I've never made extruded pasta, but my understanding is that "fresh", or flat pasta is generally made with flour ("00" is great, but the difference between that and AP flour is barely perceptible to me) and eggs or egg yolks. You can make it with water, or add semolina, but generally the "purpose" behind making fresh pasta in this way is so you have a very smooth, silky noodle for your tagliatelle or whatever. Commercial pastas, which are generally extruded, are made with semolina and water and dried. Both the roughness of the semolina and the extrusion process create a nice porous surface to capture any sauce. I'm not sure how this translates into home extrusion. I think it would be interesting to try a silky style (egg yolk and 00) but who knows, maybe it gets stuck in the extruder, or is too soft to hold a shape. I know I've found that the Italian traditions generally incorporate centuries of culinary wisdom.

When I make pasta, it's always flour and water, or flour and egg. I've never used 00, only semolina and/or unbleached all purpose flour. I don't measure or weigh, I just go by "feel," so I don't have a recipe.

Here's a flour-and-water version with photos and details: http://www.hungrycravings.com/2009/12/adventures-in-extruded-pasta.html

thirschfield uses two flours in his farfalle, along with a drop of olive oil in his excellent recipe: http://www.food52.com/recipes/8525_farfalle

My KitchenAid manual isn't where it should be, and I can't remember if there are two different recipes for flat and extruded pasta doughs. Do you have an owner's manual at hand?