I have also worked as a contractor (In Denmark, though). Working as a contractor in software development is rather forgiving, as there are only insignificant expenses. Therefore I can report most / all of my revenue as profits and pay full income tax. Knowing the basics of the Danish tax code, I can estimate my contribution and just pay it on a monthly basis to SKATs (Danish IRS) bank account. EOY I will report all my deductions, banks report all my capital gains, etc. and SKAT calculates the tax true rate and automatically pays me back within a week. If I forgot something, I can change merely change my reporting and everything is recalculated instantly.

However, hearing about the systems in other countries makes me appreciate the Danish system.