The first one of these I knit was the green one (which is why it isn't in the picture on the front page) and I decided to felt it by hand so I could compare how the different cups made with Cascade 220 would look felted by hand versus by machine.
I have to say that it took a long time to get anywhere with this, and it was probably a 20 or 30 minute process to get the cup felted to the point I wanted. I put a glass measuring cup (like a big shotglass) in the cup while it dried to make the base more defined.
I started with a bucket of hot water with some wool wash in it and alternated between that and cold water rinses a couple of times, and agitated it with my hands in rubber gloves.
That said, I do like the way this one came out the best. It's the firmest and most consistently lost stitch definition. That was probably the biggest surprise for me with this experiment --in some places the stitches are completely gone and in others on the same project they're still pretty crisp.