I bought my Janome 6600 specifically for the needle up/down. I thought the thread cutter was neat, and at first I kept forgetting to use it but now I use it constantly - sometimes when I shouldn't (when quilting and what I really wanted to do was pull the thread to the top so I could bury it!!).
There are some features that I don't ... and probably won't use ... knee lift and needle threader. Oh, I never use the start button when piecing, but sometimes I do for quilting.