Excel shortcuts
I've used VMWare + Excel running on WinXP and now Windows7 for years without much trouble. In general, it's stable and fast on a mid-range 2008 iMac with 6 GB of RAM. Because I'm not a heavy windows user these days (I just fire up VMWare when needed) I don't save any files to the windows environment. Instead, I save all files back to the mac side and let time machine back them up. This is actually pretty cool, because you can treat the windows environment as a "disposable shell": I keep a backup on a large external drive (the win image is about 50 GB, and changes all the time, so you'll probably want to exclude this from Time Machine) and when things go wrong on Windows (every year or so...) I just throw it in the trash and grab a copy of my backup. In a twisted way, it's actually better than windows
All that said, I use Excel 2011 daily on the Mac and, for casual use, it works great. With larger files, you will notice slower performance, but for many things, it's absolutely fine.
Excel for Mac is much slower and missing a few of the key keyboard shortcuts I use every day -like F2 to edit a cell, ALT + to total a column of numbers, etc.
However, all of the shortcuts that make excel a breeze on windows are not as apparent on the Mac.
The shortcuts do cause some headaches, mostly because there are so many to keep track of. However, most shortcuts do exist on both platforms, they are just sometimes different for the same action. I have a (nearly) complete side-by-side list here:
https://exceljet.net/keyboard-shortcuts
[full disclosure: I created that list of shortcuts. I'm always looking to add or update, if you know of others]