Wayne's got a post on proper attire for bizblogging, and I'd like to take it one step further.
If you get yourself an appearance on radio, that's another place where you can promote your books without too much concern about sartorial splendor. Many radio programs -- even local ones -- do their interviews by phone. I've been on the air in a lot of places from England to Oregon to Florida and never left the office!
And if you're wondering, most often a t-shirt and "comfortable" shorts are the dress code.