My experience is that Office 2011 for Mac comes close enough to office 2007 to be somewhat useful in OSX. If you work on one document that you begin and finish it works. If it is a collaborative work it is a pain. I ended up installing an XP VM and using Office 2007 because I couldn't stand all the little troubles of combining the work from Windows office and the for Mac Version. If you are a university student and you have to write long papers with many colleges it works brilliantly easy if everybody uses Windows Office, but a office for Mac creates all kinds of time consuming annoying little things.
Also Office 2007 scrolls smooth in the XP VM or in bootcamp Win7. Office 2011 is for some reason much slower. Everything takes longer. It is not so bad that everybody will even notice but it is definitely a big difference especially with big documents.
Also just running Word in the background takes a big toll on battery life. I never get more than 4-5h with Word running. Without but with Browser, pdfs ... it gives me 6-8h, even if Word sits idle doing nothing.
The interface is much worse although 2011 is a big step forward.
If you really know your way around in the Office for Windows you just need to understand that Office for Mac is a cheap copy and neither works as well nor offers nearly all the features. It is like a new Office with a similar interface but in general 3 generations behind.
For big stuff and collaborative work I still start up the VM as 2007 is much superior even though it is in theory older. For small stuff 2011 works too and still offers more than iworks which is quick but I cannot get used to this old interface and to work as quick I would probably need to learn a bunch of short cuts. The mouse interface in iworks is either very inefficient or not very intuitive, probably both.
