I just read an article about a guy that claims to be the most tax efficient man in America. He is a CPA with a fascinating story that I urge you to read. Here is the pertinent paragraph from the story:
Tax rules allow him to work for only three days of a 11-day trip and write off the airfare and a majority of other costs, he says. "To deduct the airfare, you have to spend more than half your working days on business, but travel days don't count, and neither do weekend days you wouldn't work anyway," says Mr. Stives. "So I can leave on a Friday, teach for three days midweek, and return the following Monday."
Here is a link to the article:
http://custom.yahoo.com/taxes/article-112485-2306a83f-c6fe-3fe5-af62-1d7e48c47870-most-tax-efficient-man-wsj