The biggest non-game hole in the Linux repertoire is a solid replacement for Project. Unfortunately, no one is working on one.
The games issue does turn a lot of younger “power users” off of linux, but Steam’s new OS due out soon should help a lot there, since many of their bigger titles will probably get ported to it eventually (and thus onto most other Linux platforms as well).
One other thing to be aware of, especially with regards to the OpenOffice/LibreOffice replacement for MS Office: the open-source versions try very hard to conform to the standards for document handling. MS does not, so any document you create in Linux is likely to look messed-up when opened in Windows. Installing the MS fonts helps, but it doesn’t solve everything.