My wife and I recently took a trip to visit relatives and we had our first introduction to airline baggage fees. I knew in advance that airlines were charging fees but we decided to check bags anyway. I understood that the airlines charge around $20 for a bag so I figured that wasn't a big deal. Course for some reason I didn't realize they charge the fee both directions on a two way flight, for two people its twice as much and the actual fee was $25 so it ended up being $100 for the both of us round trip. I really don't know why I didn't expect they'd charge the fee both directions, but they do. That made my expected $50 actually $100. A $100 fee for bags seems like a lot. But if the tickets had been $50 extra each then I wouldn't have balked at that.
Generally I think if the airlines charge fees for ala carte extras then that is fine with me. Checking bags is not necessary for everyone and I see no problem with the airline charging extra for it. If you use it you pay and if you don't you save the money. If you want to save the money then pack light, its really as simple as that with few exceptions.
It seems that almost all of the airlines are now charging fees for checked bags. The site Airfarewatchdog has a summary list of arline bag fees. Its a couple months out of date so it is probably best to check the airline directly for current fee rates.
The only thing I really don't like about this policy is that is if you do decide you want to check bags then it makes price comparison when shopping for airfare a little more difficult. You can't just search for fares and compare the prices you also then have to find out the bag fees and add that on top to get the real price.