It was only a few weeks ago that United Airlines announced it would start charging passengers $50 for a second checked bag on return flights, the next airline to follow suite is US Airways.

US Airways spokeswoman Valerie Wunder said the fee comes partly because of higher fuel costs, but she said it will generate an estimated $75 million in revenue and cost savings each year. United has said the new fee will total more than $100 million in additional revenue.
"The main reason we did this was to mitigate costs," Wunder said. "With fuel at $100 a barrel, we needed to realize that reality and do something other than just raise fares."
Both US Airways and United Airlines second checked bag change will take effect for travel after May 5 2008, with the change being applied to tickets on US Airways purchased from Tuesday 26 February 2008 (United Airlines started applying this charge on ticket purchased after 4th Feburary)
I and other experts don’t expect this trend to stop here, as with most trends in this industry, such as ticket price increases, and additional fuel charges I am expecting airlines based in both the US and overseas to follow suit, over the coming months.
Ultimately though it’s the passengers that will determine how many airlines adopt this new change, if enough of the flying public boycott these airlines, others might think twice before adopting this new charge.