For OO.org no more hassle than MS Office! In fact less as you can just go download it for free

OpenOffice is fine on Linux and Windows as well, you've a quite good and stable suite. "Compatibility" is improving, you've usable documents, you can open/read/write Office documents (even from 2007 suite). I'm using Openoffice mainly because I use two PC at work, one with Windows, one with Linux, OpenOffice is a requirement if I wanna work with my own documents as well as with my colleagues (using Win)
If you're primarly using Excel and Word you've good chances of a very good interoperation but it's not so perfect as it could be, you know, when you deal with closed formats without doc you don't have 100% interoperability (courtesy of MS).
Powerpoint is improving, word and excel are more mature