The 24-hour limit was a real pain when you went on vacation, so one week is much better.
But there's a downside for those who suffer from competition! I've had someone flood the market with too-low prices, so I keep my prices up at what I think is reasonable. Then, if that person didn't get logged in one day, then I would have some sales sneak through. That's nearly impossible now! :(
I thought I would appreciate having multiple toons selling, too, but it turns out I don't use the feature. It's the same problem as before - you don't want your high-level adventuring toons to be selling, because you don't want to have to come back to town all the time to check your sales. I still use my low-level "selling" toon for all sales, since he has the mansion with the six selling slots! :) And he never leaves town anyway!
Maybe when I get my veteran's display cases (about the time RoK comes out! :) ), then it will make more sense to sell from multiple toons. As I understand, you can get one veterans case for each toon on the account, but since only one could sell at a time (before), the others were wasted!