Seriously, stop moving my buttons. I hate it when I get a new piece of software comes out and all they really did was move everything around so people would think it warrants a new major release. Probably it also did warrant that but it would be something major that has changed under the covers. And to make sure people notice and buy their new product they just move things around.
Just look at the Firefox 3.5 to Firefox 4 move. The only thing I noticed that changed and stuck with me was that everything moved to somewhere else. Soon after that I made FF 4 look like FF3.5 again because I was used to it for a while. For some reason someone also changed the order of the contextmenu and "Open in new tab" is now first in that menu instead of "Open in new window". So the first couple hundred times I was opening things in new windows instead of tabs. That annoyed me to bits. There was probably a good reason to do it. But from a users perspective I did not see it.
I don't think you should change things after a while just for the sake of changing. Your button might not be in the very best place but after seeing it in that place for years, people will get used to it.
It would be like changing the order of the pedals in your car. Or changing the order of the gears.
Don't forget your users use your product every day and they get used to the quirks. Take those quirks away and you will some of their productivity for a while and annoy them. Perhaps even enough to try something new.
That's not to say that in some cases it will be useful. But in the case of the browsers like FF3 to FF4 and IE8 to IE9 I think it was just done to show the users their was a reason to upgrade because it looked different. These browsers have been doing pretty much the same thing for the last couple of years with the same buttons. They just have newer and better engines and some never used options.
So stop moving my buttons and we will be friends again.
I understand noone will agree with me and everyone has an opinion, this was just mine, so there.