How well does Wine Work for most Windows applications?
Wine (Wine is Not an Emulator) is not an emulator (if you didn’t gather that deduction from the acronym definition). Don’t expect it to emulate. It provides an application compatibility layer for Windows programs.
Wine supports many programs. Most programs that are most successful are not graphics intensive — integrating support for graphic programs and DirectX seems to be the biggest problem in Wine right now. There are some programs that just are not going to work in Wine.
Winehq.org (Official Wine website) provides an Application Database in order to help you determine if a program will work under Wine, or what things you can do to make it work properly. If you are considering switching to Linux and want to check to see if your current [absolutely necessary] applications will run on Linux, check the AppDB. Be sure to look under the details about the program to see if any specific features [which you may or may not need] don’t work, or don’t work especially well.
Wine is compatible with Linux, Solaris, and MacOS — heck, there’s even a Windows version of it (I assume for developers).