There few windows programs that doesn't have a good or better equivalent in osx. But there are many quality mac programs that you can't find in windows. I speak as a person who runs a business and as a programmer.

The only thing I miss from windows is visual studio and C#. But that is no longer a problem, because with the Intel macs, you can run both windows and osx.

For example, I have a Core 2 duo windows pc, but I like working on my old mac, G4 ibook, better.