I worked from home (as a full-time employee of various companies) for 12 years, and I 100% disagree with the point made here and by the various commenters. A huge part of the benefit of working at home is being able to use my time in a way that works as efficiently for me as possible, and that means spending the time of day when I'm sharpest (early morning) working, not taking a shower and getting dressed. I generally took a shower and got dressed around lunchtime, which provided a nice boost from the early afternoon need-a-siesta feeling.

If showering and getting dressed first thing works for you, great, but I get really tired of seeing people dispense that advice as the "right" thing to do.