With many US airlines now charging fees for checked baggage; more and more people are trying to carry more and more luggage on to flights. American Public Media ‘s Marketplace show on National Public Radio had a great story about the problem and one industry groups proposed solution. One thing I never do and never recommend is checking your computer bag with your computer inside. In fact if I am taking a flight that involves travel on a regional carrier or i know I’ll be on a smaller plane I make sure to bring along a good laptop sleeve in the event that I have no choice but to check my bag.
A great reference for airline carry on bag allowances is at the Luggage Online merchant site.
If you travel often and want to place your computer under the seat keep in mind that back packs and briefcases usually open from the top and side so that you can get things back into your bag while it is still under the seat. Messenger bags and those with a flap over the zipper make it that harder to get items in and out while that bag is under the seat. Remember that no matter what you bag is going to be laying with one side down on the floor. Something that I’ve run into several times was a wet floor; and then a wet bag at the end of the flight. I used to place the airline provided blanket under my bag (because you never know where those blankets have been or the last time they were cleaned).