We have large commercial app that we want to convert from Delphi 6 to 2010. Approx 10 3rd party component sets, all with source code... I have heard warnings about Unicode
I must add this article from Carey Jensen to others mentioned. It is labeled: "Delphi Unicode Migration for Mere Mortals: Stories and Advice from the Front Lines" (in english). http://www.danysoft.com/free/delphiunicodemigration.pdf
As you can see in the title of it, you will find many experiences and hints and tips. I think it is the answer to your question. After carefully read it, you will sure knows what to do next. :)
Found in: http://www.danysoft.com/productos/migrar-aplicaciones-a-delphi-xe-o-cbuilder-xe.html